I have isolated the problem, I think, after noticing that it occurs 
only when my iBook is unplugged from the AC adapter.  Apparently, 
there were two separate issues


1) Power Manager

Apparently, the difficulty arises from a problem with the 
EnergySaver/PowerManager.  If you set it to any setting other than 
all the way toward "Better Performance," you will get about 1 event 
per second shortly after you stop typing.  (More precisely, the 
problem occurs only when the "Allow processor cycling" option is 
checked.)

It would be nice if the VM could (possibly optional) automatically 
unset the processor cycling option.

--------

2) New higherPerformance Preference

I also discovered that there is also a second problem, which I had 
confused and mixed with the present one.  If you pop into Morphic and 
set the preference for higherPerformance, MVC dies, processing only a 
few events at a time.  This is manifest, for example, by trying to 
click alternate entries on a browser list -- sluggish as hell. 
Resetting the preference makes the problem go away.