With the recent rash of Trackback spam, I finally bit the bullet and am now experimenting with Akismet in addition to Spam Karma. I’m not sure how well they work together, or, at this point, which plugin processes the comment first. Update: I’m trying Akismet on its own for now. Or, more precisely, Akismet as the sole second line of defense. Bad Behavior is still holding the front line.
Update (Feb 14): I’m now back to using Spam Karma 2, but with a plugin that uses Akismet as one of the score components. This seems to be working well, as SK is able to block the ridiculous stuff (100 porn links in one comment, etc.), and Akismet is able to catch the trackback spam that’s been passing SK2 by temporarily including an inbound link.
The big problem I had with Akismet was that aside from the age of the target post, the blocked comments weren’t sorted or filtered in the admin interface. I was having to look through ~30 comments a day for false positives. Spam Karma will show only the borderline comments by default, and uses a table structure that makes it easier to skim.
This way, though, I get the proverbial best of both worlds.