I updated to 4.99.8 and got the following trap this evening:

CPU 0: fatal kernel trap:

CPU 0    trap entry = 0x2 (memory management fault)
CPU 0    a0         = 0xfffffe0108266000
CPU 0    a1         = 0x1
CPU 0    a2         = 0x0
CPU 0    pc         = 0xfffffc00007ecde0
CPU 0    ra         = 0xfffffc000035f9ac
CPU 0    pv         = 0x0
CPU 0    curlwp    = 0xfffffc000fcd2660
CPU 0        pid = 335, comm = nfsio

filed as port-alpha/35448:
http://www.netbsd.org/cgi-bin/query-pr-single.pl?number=35448

I am prepared to paypal (or send a cheque) USD$20 to whomever can fix
this.  offer expires in 30 days.

coredump and debug kernel available on request.

-- 
  Aaron J. Grier | "Not your ordinary poofy goof." | agrier@poofygoof.com
              "silly brewer, saaz are for pils!"  --  virt