One thing I've noticed is what I call "blinky-light mode".  During times of
heavier-than-normal memory activity, often related to X, the system will
appear to wedge (no mouse tracking, no keyboard echo) for as much as 30
seconds or a minute.  If I look down at my disk controller status LED, it
will be flashing on and off at around .5 or 1 Hz, but I will typically not
hear a lot of seek activity from the drive.  Eventually the drive will start
seeking and everything will come back to life.

I haven't submitted any kind of bug fix for this for a couple of reasons. 
On the one hand, I haven't observed this on enough NetBSD systems to feel
I can claim it's independent of my setup (IDE disks, for example); on the
other hand, I have held off because of a suspicion that this is a
long-running bug in the Mach VM code (I saw exactly this behavior under Mach
2.6 on a Sparc 1+) and hence unlikely to be fixed quickly.

Does this match anybody else's observed behavior?

Dave Eckhardt
davide@cs.cmu.edu