Do you use something like askimet to filter the spam comments out?

I installed it on one of my blogs and it seems to catch the spam pretty well whilst letting the good comments through.

I just switched off comments. Usually the only people I've noticed commenting are spammers, and if they really want to tell me something, they can email me.

Blog commenting cannot be made illegal because you cannot specify clear lines between a genuine comment and a spam comment. Your definition of spam comment might be different than mine.

You can always prevent auto-generated spam comments by implementing simple solutions like a captcha or a question. But you will have to deal manually with spam comments that are placed by hand.

I use growmap anti-spam plugin on my WordPress blogs and on my custom blogs I have a simple math question. They are pretty effective for spam bots.

You can require visitor who want to leave comment to sign up first or can use alternate account like Facebook to comment on your post.

Sadly comment spam is getting more and more out of control. Like the suggestions above mention: enable askimet and require users to sign up before posting can cut down on a lot of it. You can also turn of commenting on posts older than a few months old since spammers target higher pagerank posts which will be older posts on a blog. All new posts will be Pagerank N/A until a pagerank update which occurs every few months or so..

Yes, I agree. Just be more strict and require the readers to sign-up first.
This is the only way to lessen these annoying spammers.

Fluff brings up the problem in a nutshell. Who do you prosecute? If someone buys a service for SEO and doesn't realize until too late their methods are spammy - do you go after the person who got duped by the service? How do you know if it was a service they used or the individual poster that has committed the offense.

Prosecuting anyone who spams a blog even though they had no reason to believe that the service they contracted uses spam techniques will have only one repercussion - it will stop people from using SEO services completely and a lot of honest businesses will get trashed. I'd love to see spam services shot down, but in this economy I don't think having honest businesses trashed just because there are scumbags who are scammers in the same field is a very good idea.

Just make it so that no one can comment on your posts. Problem solved.