Make sure you profit off of the referrals. Edit to elaborate: Since you specifically mentioned referral models that give credits, read what I just wrote about

Make sure you profit off of the referrals. Edit to elaborate: Since you specifically mentioned referral models that give credits, read what I just wrote about Linode's referral model above (http://news.ycombinator.com/item?id=2048246 http://news.ycombinator.com/item?id=2048246)