I switched my antispam tool from Spam Karma 2 to Akismet last week - wanting to play with Matt's new toy, and see how a distributed spam blocker would work out.
Generally, it was pretty good. But, I had to moderate several comments. I've almost never had to do that under SK2 - it just works, totally, and invisibly.
But, I just checked my WordPress dashboard, and saw an interesting item: Owen Winkler: Spam Karma 2 Akismet Plugin BETA. Hmmm... Akismet as a plugin for SK2? Cool!
Turns out, SK2 will do its usual magic, and if it's still unsure about a comment, it will then feed it to Akismet for clarification. The best of both worlds! Very very cool.