Well people who utilize comment spamming on blogs are getting smarter at what they do… and to be honest there alot of people who really do not care if the spam is closley related to the topic.. why you might ask, is because most bloggers want the free content, so it looks like they have a popular blogs and so that the search engines actually come back more often, and then they come up for a whole bunch more keywords and so on…

So it works both ways… it all depends on what the comments are… but content is content at the end of the day… Might as well let the spammers help your site, as long as you have no follow links on your out going links your sweet as…

I know you posted this a while. Since then Akismet has came into existence which helps a lot. For me it wasn’t enough. Things still slip by. So I created a numbered captcha. That combined with Akismet got rid of spam completely. I made a tutorial on how I implemented it here:
http://robmalon.com/howto-eliminate-wordpress-trackback-comment-and-pingback-spam/

If you need help with it feel free to give me a shout. Spam can really be a time suck.

I do have it set to send an email when it kills a spam so I got several hundred yesterday, but I’m pretty sure this can be disabled once you trust it.