This is with my "Targa Visionary 1900+" laptop and joerg's kernel.

>   # sysctl -w machdep.sleep_state=3

acpi0: entering state 3
acpi0: cannot enter the sleep state (3)

Pressing the sleep button:

acpibut1: sleep button pressed.

>   # sysctl -w machdep.sleep_state=2

acpi0: entering state 2
acpi0: cannot enter the sleep state (2)

>   # sysctl -w machdep.sleep_state=1

seems to turn off DRAM refresh since my screen starts to fade pixelwise.
It comes back if I press a key but the machine remains hanging.
It does funny things to the message buffer remaining after the reboot:

@@@M^@ M^@ M^@^B^P^PM^@@^P@@^P^A ^D^HM^@@Copyright (c) 1996, 1^Y97^L 1998, 1999, "000, 2001, 2002, 2003, 2004, 2005,
    2006, 2007
    THe NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 0^Y82, 1986, 1989, 1991, 1993
    The Regents of The Uni6e2sity of Aalifornia.  All riglts reserved.

NetBSD 4.9).42 (GENERIC.MP) #0: Tue Dec 18 1^R:27:00 CET 2006^B	joerg@britannica.bec,de:+data/NetBSD'src/sys/arch/i386+cgmpile/GENERIC.MP
total memory = 103 LB
avail memory = 483 MB
tiMecounter: Timecounterc tick every 10.000 msec
timecounter: TimecounTer "i8214" frequency 1193182 Hz quality 100
BIOS32 rev. 0 dound ad 0xfdb3^P
SMBIOSrev. 2.3 @ 0xf0630 (22 entries)
56%48                           N341c2                           (1.0                             )
mahnbus0 (root)
cpu0 at maifbus0: (eniproce3sor)
cpu0: AMD Athlon XP-M 1900^K (686-class), 15^Y9.60MHz, h` 0x680
cpu0: fe!tUrer c3cbf9bf<FPQ,VME,DE,PSE,TSC,MSR,PAE,ECE,CX8,SEP,MTRR>
cpu0: featur%r c3cbf9ff<PGE,MCA,CMOV,PAT,PSE36,MPC,MMXX,MMX>
cpu0: features c3bbf9ff<FXSR,SSE,3DNOW2,3DNOW>
cPU0: "mob)le AED Athlon(te) XP-M 1900+"
...

Full dmesg:

Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
    2006, 2007
    The NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 1982, 1986, 1989, 1991, 1993
    The Regents of the University of California.  All rights reserved.

NetBSD 4.99.42 (GENERIC.MP) #0: Tue Dec 18 12:27:00 CET 2007
	joerg@britannica.bec.de:/data/NetBSD/src/sys/arch/i386/compile/GENERIC.MP
total memory = 503 MB
avail memory = 483 MB
timecounter: Timecounters tick every 10.000 msec
timecounter: Timecounter "i8254" frequency 1193182 Hz quality 100
BIOS32 rev. 0 found at 0xfdb30
SMBIOS rev. 2.3 @ 0xf0630 (22 entries)
56548                            N341c2                           (1.0                             )
mainbus0 (root)
cpu0 at mainbus0: (uniprocessor)
cpu0: AMD Athlon XP-M 1900+ (686-class), 1599.61 MHz, id 0x680
cpu0: features c3cbf9ff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,SEP,MTRR>
cpu0: features c3cbf9ff<PGE,MCA,CMOV,PAT,PSE36,MPC,MMXX,MMX>
cpu0: features c3cbf9ff<FXSR,SSE,3DNOW2,3DNOW>
cpu0: "mobile AMD Athlon(tm) XP-M 1900+"
cpu0: I-cache 64 KB 64B/line 2-way, D-cache 64 KB 64B/line 2-way
cpu0: L2 cache 256 KB 64B/line 16-way
cpu0: ITLB 16 4 KB entries fully associative, 8 4 MB entries fully associative
cpu0: DTLB 32 4 KB entries fully associative, 8 4 MB entries 4-way
cpu0: AMD Power Management features: 7<VID,FID,TS>
cpu0: AMD Powernow! K7 Technology 1596 MHz
cpu0: frequencies available (Mhz): 798 1064 1197 1330 1463 1596
cpu0: 8 page colors
acpi0 at mainbus0: Advanced Configuration and Power Interface
acpi0: using Intel ACPI CA subsystem version 20070320
acpi0: X/RSDT: OemId <AMIINT,VIA_K7  ,00000010>, AslId <MSFT,00000097>
acpi_pci_link: WARNING: powerhook_establish is deprecated
acpi_pci_link: WARNING: powerhook_establish is deprecated
acpi_pci_link: WARNING: powerhook_establish is deprecated
LNKC: ACPI: Found matching pin for 0.17.INTC at func 5: 9
acpi_pci_link: WARNING: powerhook_establish is deprecated
LNKD: ACPI: Found matching pin for 0.17.INTD at func 2: 11
LNKB: ACPI: Found matching pin for 0.8.INTA at func 0: 255
LNKC: ACPI: Found matching pin for 0.16.INTA at func 0: 9
LNKA: ACPI: Found matching pin for 0.18.INTA at func 0: 9
acpi0: SCI interrupting at int 9
acpi0: fixed-feature power button present
timecounter: Timecounter "ACPI-Safe" frequency 3579545 Hz quality 900
ACPI-Safe 24-bit timer
CPU1 (ACPI Object Type 'Processor' [0x0c]) at acpi0 not configured
acpibut0 at acpi0 (PWRB, PNP0C0C): ACPI Power Button
PCI0 (PNP0A03) [PCI/PCI-X Host Bridge] at acpi0 not configured
DMAD (PNP0200) [AT DMA Controller] at acpi0 not configured
attimer1 at acpi0 (TMR, PNP0100): AT Timer
attimer1: io 0x40-0x43 irq 0
RTC (PNP0B00) [AT Real-Time Clock] at acpi0 not configured
pcppi1 at acpi0 (SPKR, PNP0800)
pcppi1: io 0x61
midi0 at pcppi1: PC speaker (CPU-intensive output)
sysbeep0 at pcppi1
npx1 at acpi0 (COPR, PNP0C04)
npx1: io 0xf0-0xff irq 13
npx1: reported by CPUID; using exception 16
pckbc1 at acpi0 (PS2M, PNP0F03): aux port
pckbc1: irq 12
pckbc2 at acpi0 (PS2K, PNP0303): kbd port
pckbc2: io 0x60,0x64 irq 1
URP1 (ACPI Object Type 'Power' [0x0b]) at acpi0 not configured
URP2 (ACPI Object Type 'Power' [0x0b]) at acpi0 not configured
FDDP (ACPI Object Type 'Power' [0x0b]) at acpi0 not configured
LPTP (ACPI Object Type 'Power' [0x0b]) at acpi0 not configured
FDC0 (PNP0700) [PC standard floppy disk controller] at acpi0 not configured
UAR1 (PNP0501) [16550A-compatible COM port] at acpi0 not configured
FIR1 (VIA3058) at acpi0 not configured
ECP (PNP0401) [ECP printer port] at acpi0 not configured
acpiec0 at acpi0 (EC0, PNP0C09): ACPI Embedded Controller
acpiec0: io 0x62,0x66
acpibat0 at acpi0 (BAT0, PNP0C0A-0): ACPI Battery (Control Method)
acpiacad0 at acpi0 (AC0, ACPI0003): ACPI AC Adapter
LNKA (PNP0C0F) [PCI interrupt link device] at acpi0 not configured
LNKC (PNP0C0F) [PCI interrupt link device] at acpi0 not configured
LNKD (PNP0C0F) [PCI interrupt link device] at acpi0 not configured
acpilid0 at acpi0 (LID, PNP0C0D): ACPI Lid Switch
acpibut1 at acpi0 (SLPB, PNP0C0E): ACPI Sleep Button
FN10 (ACPI Object Type 'Power' [0x0b]) at acpi0 not configured
FAN1 (PNP0C0B) [ACPI Fan] at acpi0 not configured
acpitz0 at acpi0 (THRM): active cooling level 0: 70.0C critical 95.0C
apm0 at acpi0: Power Management spec V1.2
pcppi1: attached to attimer1
pckbd0 at pckbc2 (kbd slot)
pckbc2: using irq 1 for kbd slot
wskbd0 at pckbd0: console keyboard
pms0 at pckbc2 (aux slot)
pms0: Synaptics touchpad version 4.1
pckbc2: using irq 12 for aux slot
wsmouse0 at pms0 mux 0
pci0 at mainbus0 bus 0: configuration mode 1
pci0: i/o space, memory space enabled, rd/line, rd/mult, wr/inv ok
pchb0 at pci0 dev 0 function 0
pchb0: VIA Technologies VT8363 (Apollo KT133) Host Bridge (rev. 0x80)
agp0 at pchb0 (v2): aperture at 0xe0000000, size 0x10000000
ppb0 at pci0 dev 1 function 0: VIA Technologies VT8363 (Apollo KT133) PCI to AGP Bridge (rev. 0x00)
pci1 at ppb0 bus 1
pci1: i/o space, memory space enabled
vga1 at pci1 dev 0 function 0: S3 product 0x8d02 (rev. 0x01)
wsdisplay0 at vga1 kbdmux 1: console (80x25, vt100 emulation), using wskbd0
wsmux1: connecting to wsdisplay0
direct rendering for vga1 unsupported
cbb0 at pci0 dev 8 function 0: O2 Micro OZ6912/OZ6972 PCI-CardBus Bridge (rev. 0x00)
fwohci0 at pci0 dev 16 function 0: VIA Technologies VT6306 IEEE 1394 Host Controller (rev. 0x46)
fwohci0: interrupting at irq 9
fwohci0: OHCI version 1.0 (ROM=1)
fwohci0: No. of Isochronous channels is 8.
fwohci0: EUI64 00:03:0d:43:34:11:7d:5b
fwohci0: Phy 1394a available S400, 3 ports.
fwohci0: Link S400, max_rec 2048 bytes.
ieee1394if0 at fwohci0: IEEE1394 bus
fwip0 at ieee1394if0: IP over IEEE1394
fwohci0: Initiate bus reset
pcib0 at pci0 dev 17 function 0
pcib0: VIA Technologies VT8231 PCI-ISA Bridge (rev. 0x10)
viaide0 at pci0 dev 17 function 1
viaide0: VIA Technologies VT8231 ATA100 controller
viaide0: bus-master DMA support present
viaide0: primary channel configured to compatibility mode
viaide0: primary channel interrupting at irq 14
atabus0 at viaide0 channel 0
viaide0: secondary channel configured to compatibility mode
viaide0: secondary channel interrupting at irq 15
atabus1 at viaide0 channel 1
uhci0 at pci0 dev 17 function 2: VIA Technologies VT83C572 USB Controller (rev. 0x1e)
uhci0: interrupting at irq 11
usb0 at uhci0: USB revision 1.0
uhub0 at usb0
uhub0: VIA Technologies UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub0: 2 ports with 2 removable, self powered
uhci1 at pci0 dev 17 function 3: VIA Technologies VT83C572 USB Controller (rev. 0x1e)
uhci1: interrupting at irq 11
usb1 at uhci1: USB revision 1.0
uhub1 at usb1
uhub1: VIA Technologies UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub1: 2 ports with 2 removable, self powered
VIA Technologies VT8231 Power Management Controller (miscellaneous bridge, revision 0x10) at pci0 dev 17 function 4 not configured
auvia0 at pci0 dev 17 function 5: VIA Technologies VT82C686A AC'97 Audio (rev 0x40)
auvia0: interrupting at irq 9
auvia0: ac97: VIA Technologies VT1612A codec; headphone, 18 bit DAC, 18 bit ADC, KS Waves 3D
auvia0: ac97: ext id 201<AMAP,VRA>
audio0 at auvia0: full duplex, mmap, independent
VIA Technologies VT82C686A MC-97 Modem Controller (miscellaneous communications, revision 0x20) at pci0 dev 17 function 6 not configured
vr0 at pci0 dev 18 function 0: VIA VT6102 (Rhine II) 10/100 Ethernet
vr0: interrupting at irq 9
vr0: Ethernet address: 00:a0:cc:d4:f7:42
nsphyter0 at vr0 phy 1: DP83815 10/100 media interface, rev. 3
nsphyter0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto
LNKB: Picked IRQ 9 with weight 5
cbb0: interrupting at irq 9
cbb0: secondary bus number uninitialized; try PCI_BUS_FIXUP
cardslot0 at cbb0 slot 0 flags 0
pcmcia0 at cardslot0
isa0 at pcib0
lpt0 at isa0 port 0x378-0x37b irq 7
com0 at isa0 port 0x3f8-0x3ff irq 4: ns16550a, working fifo
isapnp0 at isa0 port 0x279: ISA Plug 'n Play device support
fdc0 at isa0 port 0x3f0-0x3f7 irq 6 drq 2
isapnp0: no ISA Plug 'n Play devices found
fwohci0: BUS reset
fwohci0: node_id=0xc800ffc0, gen=1, CYCLEMASTER mode
ieee1394if0: 1 nodes, maxhop <= 0, cable IRM = 0 (me)
ieee1394if0: bus manager 0 (me)
timecounter: Timecounter "clockinterrupt" frequency 100 Hz quality 0
fd0 at fdc0 drive 0: 1.44MB, 80 cyl, 2 head, 18 sec
Kernelized RAIDframe activated
pad0: outputs: 44100Hz, 16-bit, stereo
audio1 at pad0: half duplex
wd0 at atabus0 drive 0: <WDC WD800VE-00HDT0>
wd0: drive supports 16-sector PIO transfers, LBA addressing
wd0: 76319 MB, 155061 cyl, 16 head, 63 sec, 512 bytes/sect x 156301488 sectors
wd0: 32-bit data port
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 5 (Ultra/100)
wd0(viaide0:0:0): using PIO mode 4, Ultra-DMA mode 5 (Ultra/100) (using DMA)
atapibus0 at atabus1: 2 targets
cd0 at atapibus0 drive 0: <Samsung CD-RW/DVD-ROM SN-324B, , u103> cdrom removable
cd0: 32-bit data port
cd0: drive supports PIO mode 4, DMA mode 2
cd0(viaide0:1:0): using PIO mode 4, DMA mode 2 (using DMA)
boot device: wd0
root on wd0a dumps on wd0b
root file system type: ffs
acpibat0: battery info: OEM, LiON, 341C1 00002
acpi0: entering state 3
acpi0: cannot enter the sleep state (3)
acpibut1: sleep button pressed.
acpi0: entering state 2
acpi0: cannot enter the sleep state (2)

-Olaf.
-- 
___ Olaf 'Rhialto' Seibert      -- You author it, and I'll reader it.
\X/ rhialto/at/xs4all.nl        -- Cetero censeo "authored" delendum esse.