Lately, I've been having a problem where a relatively current
   kernel will hang after a period of high load.  It hangs such that you
   can press return exactly once on it's various terminals, but any
   further keystrokes (besides L1-A) are ignored.  DTR is also dropped on
   the line that has the modem when this happens.
   
   	Is there any way I can determine where it's wedged like this?
   Any ideas on where it would be wedged?

compile DDB into the kernel and find out the kernel stack trace ?