Your question is a bit vague, I guess.  (^&

Which version of NetBSD/amd64 are you looking at (well, you said the
"snapshot", but I haven't checked its version)?

And "stable and usable" for what?

I've been using NetBSD/amd64 for about a year.  It's had more and less
good times.

 * Lack of support for some of my hardware at first.  E.g., no DMA
   support for the hard drive.  This wasn't fatal, but as I recall it
   was a whole lot faster to do *everything* via NFS from an i386 than
   to use the local hard drive.

 * I have had to turn off IOAPIC in my kernel config and build a custom
   kernel in order to keep my hardware all configuring and to keep it from
   dying (losing interrupts) during normal use.  I have never seen this
   officially fixed; the GNU/LINUX kernel, at least around January 2004
   or so, actually disabled IOAPIC if it detected this motherboard
   chipset that I'm using.  (nVidia nForce3.)

   Avoid nVidia's motherboard chipset if you can.  )^&

 * I've had two memory modules go bad on me.  I'm now on my third, and
   keeping my fingers crossed.  This is just flakey hardware and nothing
   to do with NetBSD.

 * X loses mouse button events if the mouse is moving while the button
   is clicked/released.  I believe that M. Bouyer(sp?) confirmed that
   he also saw this on the Alpha, so it is believed to be a general
   X problem, not a NetBSD or AMD64-specific issue.  (But it certainly
   does not manifest with my i386 boxes---same mice.)

 * Similarly, I've noticed that occasionally CapsLock releases have been
   lost, though I can't correlate them to mouse motion.  I never had
   this with the i386, and have an i386 laptop that is running a not-too-
   distant -current.  (I can't get the laptop fully up to date due to
   another issue that I haven't the expertise to quickly solve and that I
   have not yet been able to even *slowly* solve.  (^&)

Presently, my system is pretty stable, though the particular revision
I am on (2.99.10 kernel or so) tends to sporadically seize up.  I did
not experience that with older kernels.  It has not got to the point that
I've bothered trying to build a new kernel in the hopes of fixing this
issue.

I use my AMD64 as my primary system.  The biggest annoyance I've had is
having to adjust to using links-gui as my graphical browser.  links has
its virtues, but I didn't like being forced to change.  (^&  (No other
graphical browser I've tried has worked for me under NetBSD/amd64.
See a recent thread on this list.)

I do not run any of the 2.0 release candidates on my AMD64 box,
however.  I expect that I'll continue to track -current for a while,
so my experiences may not be directly relavent to your question.
Still, it's an answer of sorts.  (^&

-- 
  "I probably don't know what I'm talking about."  http://www.olib.org/~rkr/