I noticed that a few build proceses hung when I attempted to kill them via 
Ctrl-C.  Eventually a ps -xa hung, and well, the processes that hung were 
listed in ps, but kill said they didn't exist.   A reboot command panic'd 
the kernel.  Here's the trace:

panic: uvm_fault_unwire_locked: unwiring non-wired memory
Stopped in pid 145 (ntpd) at _kdbprinttrap+0x5a:	unlk	a6
...
kdbprinttrap
panic
uvm_fault_unwire_locked
uvm_unmap_remove
uvm_unmap
uvm_deallocate
exit1
syssys_exit
syscall(1)
trap0

Hmm... maybe it's time to get a disk so I can at least keep a kernel dump.

- alex