>Our SPARC running NetBSD has been crashing, reliably, every night.  The
>stack traces vary, but they always have one thing in common: the
>deepest few frames on the stack are always
[...]

  This might be totally unrelated, but a few of my NetBSD/i386 machines
were crashing each night, a problem I finally traced to the local 
network's time service.  Some other machines on the net were becoming
master timed servers and then changing the time willy-nilly:  a few hours
ahead, a few back, etc, until something gave and my machine crashed.  Once
I got those machines to stop doing that,  my late-night mystery crashes
ceased.   But until then, the crashing was reliable. :) 
Just a thought.

Dave Deaven