Some people on Apple's forms have said that removing all non-standard characters from your own name/login name worked, but that doesn't apply to me.
What's worked for me now was killing the pref files, then not logging into anything (so it doesn't crash when it first starts). Then disabling all sounds in the Preference panel. Then go turn back on AIM/.Mac and Rendezvous.
I'm not sure why this solves it. At least it hasn't crashed in the past hour or so.