Here’s a spam blocking tip for ya!
If you get lots of comment spam and DO have the Akismet plugin installed and updated in your WordPress, check the dates of the posts that the spam-comments are being left on. Chances are high that much of the spam is left on older posts. I guess the spammers figured we wouldn’t notice?
Take a look at the Discussion settings from the WP main menu. Note under Other comment settings the third line down where you can fill in the number of days after which an article can’t be commented on.
Fill in some value less than 30 days and that will knock down the number of spam comments left on your blog. Don’t forget to scroll down the discussion settings page and hit the Save Changes button.
There is at least one alternative WordPress plugin (and there’s probably many more, but I haven’t needed to check for any) that was commented on in a positive way, called WP-Spam Free. Might be worth checking out.