Buying leads doesn't really work for me. I tried co-reg once, and I think I made 1 sale out of over 400 leads. Of course, the product may have something to do with it. I have more success with PPC. By building a list from scratch, I can convert at about 1 in every 100 leads or so.

Lesson here is that targeted traffic + good relationships work

Problem with most email leads is that they are not targeted, and it's very hard to build a relationship with them. They will probably hate you for sending them spam mails.