I have my own home-brewed captcha on my WP blog. I was running 2.0.2 up until today and I was getting maybe 1 spam comment a day (all my comments go into moderation). However, I just upgraded to WP 2.0.3 today and suddenly, within a minute of fully upgrading the site, my blog started getting swarmed with spam comments (>100 in one hour).
Things seemed to have cooled off now, and all comments only made it moderation, not to my blog, but I'm trying to figure out why this might have happened? Do spammers somehow track when you upgrade a site? How might this have happened?