I created a little performance counter for myself to use locally, you guys are welcome to try it.
Satoshi, maybe you could integrate this or something similar and put an option in there to turn it on/off? It spams up your debug.log and shows the performance of each thread.. it also shows on the UI in the status bar where it used to say ‘Generating’.
Patch: http://heliacal.net/~solar/bitcoin/bitcoin-svn-79-perfcounter-2010-06-02.patch
Screenshot: