I woke up this morning to find that about 150 spam comments, all variations of about half a dozen different comments, were posted to a single entry on this blog. Obviously my blog's spam filter needs a little bit of tuning, but this is ridiculous. What's the best way of dealing with unwanted spam these days?
Turn comments off on entries older than X weeks. I have X at about 2 or 4, somewhere around there. That gets rid of 90-95% (guessing) of the spam the blogs I host receive. Turn on comment moderation. Regularly flag all unpublished comments and delete them. You can probably do that last one with a SQL script. The first one (turning off comments on older entries) pretty much has to be done with a SQL script, but it's easy; you'd figure it out faster than I could write it down.
Try Akismet. It's caught hundreds of spams on my blog with nary a single false positive. http://akismet.com/
Disabling comments on entries older than X weeks works fantastically well.