I've discovered what appears to be a correlation between console
output and seemingly random panics.  When doing a trivial execution
which does a lot of output, such as:
	# cd /usr/src
	# make build >&BUILD& tail -f BUILD
the console will definately stop accepting keyboard input before
the build completes.  To further complicate things, if it doesn't
also panic the system, a panic can be "encouraged" by suspending
the tail(1) process and performing something else that outputs
data, such as dmesg(8).

If I avoid all console output on the serial console, I can have
a kernel running for days on the INDY (this one is an R5K).
If I DO perform much work which outputs to the serial console,
that time is cut down to hours, if not minutes.

I don't have any captures of the panics, sorry.  They're usually
something along the lines of "TLB" and "out of universe" or 
such strange things.  I'll start capturing the panics as they 
occur, however I'm avoiding crashing the machine due to the
amount of fsck'ing and damage that occur since I'm doing
constant software builds for snapshots.

Nonetheless, I wanted to present this bit of information as
food for thought.  Perhaps it might pique someone's interest
in the meantime to see if they can duplicate the problem with
kernels (has been happening from as far back as I can 
remember, namely netbsd.IP22, and continues to date with a
current kernel).

More as I discover...
-scott