well crap. I'm in the same boat. I was on 4.0 still, and jailbroken fine. But then I wanted to do the commcenter hack to enable tethering, and the deb file wanted 4.0.1 firmware, so I went to update to 4.0.1 and rejailbrake. itunes updated me to stock 4.0.1 no problem, but safari keeps crashing when I try to jailbreakme.com again. clearing cache/cookies didn't help. I'm trying to restore from backup to see if that helps before i set up as a new phone as suggested above.