I recently migrated all my blogs to WordPress 3.0. One of the things you do is temporarily disable all plugins including Akismet spam filter. During the short period of time the spam filter was off I received, and had to later kill, more spam than I would normally receive in a week. And don’t get me wrong this blog constantly receives a moderate amount of spam , which Akismet usually blocks. My site stats reflected the uptick in spam, with a huge spike in visits on the day the spam filter was off. So it would be a good hypothesis that some spammers are able to detect blogs with Akismet and just leave them alone and spend the fraction of a cent it costs to send their toxic crap elsewhere. If this is true, Akismet is not only an awesome spam filter, but it also serves as a deterrent, which is even better. Anyone can confirm or deny if this is true or offer any explanation why I got so many visits exactly when my spam filter was off?