I've been running wp1.5 for a while, and decided that it was finally time to join 2006, so I upgraded to 2.0.3 this weekend. The hashcash is something that has always worked excellently in blocking comment spam under 1.5, but with this upgrade, it doesn't seem to be working. That is, I've found about 15 spam comments since I upgraded ~18 hours ago.
Has anyone else encountered configuration problems from upgrading, or something of this nature? I shudder to think the spammers have finally worked up a bot that can actually perform the requisite calculations to pass the blocker test.