Taking my inspiration from Andy Beard's great Niche Marketing blog, I've created a Comments Policy for NetMarketingChaos.com.

The elevator pitch version of it is that I don't use nofollow on any comments, but I have some basic conditions for accepting them. Nothing too strict, just some simple guidelines to keep the site from getting overrun with spam.

Basically, if your comment has value it's probably going to be approved (and you'll get another link back to your site).