I've deleted some that actually post comments on the blog post but their screen name or email/website are not my deal....

I don't want to offend anyone who finds the crap I write good, but....

visits blogs if linked before approving. Most I can tell but some are iffy. In fact I copy /paste the url so they dont see where i came from

well where the incoming traffic came from. i know they see IP's

I immediately delete obvious ones and wait a few days to delete any that seem iffy.

figures if I'm wrong about the iffy, the person probably won't go back to find out if their comment is still there

Automated sites? Delete. Links in a comment, unless it's someone I know and/or germaine to the discussion? Delete.