I also noticed the problem where 'w' just wouldn't work anymore.
Then, groping around in /usr/lib, I noticed I had libkvm.so.4.0, *and*
libkvm.so.5.0.  Somewhere along the line I did a 'cd libkvm' and built
the "new" stuff, and all subsequent make builds rebuilt the libkvm.old, 
but the various utilities are using libkvm.so.5.0!  (according to ldd)
Trashing the libkvm.so.5.0, and rebuilding the various utilities took
care of the problem.  So.. if you've seen this problem, check /usr/lib,
and be careful with that easy-to-use 'cdpath' variable.. :)

-Andrew