If you are getting a lot of spam comments you might want to try the new plugin from Andy Bailey / Growmap:
This plugin will add a checkbox to your comment form asking users to confirm that they are not a spammer. A nice, simple solution to reduce spam comments.
I don’t get too many spam comments on this blog but on my self-development blog I do. I used to get hundreds every day…now virtually none!
A great plugin…try it.