[zenith]

20 points = 1 credit if you haven't donated in the past.
10 points = 1 credit if you have donated at least once.

I think the most points used so far is in the 20,000 range. Only 7 or so players have actually utilized the referral program to its fullest. Posting on forums and whatnot can garner you a ton of referrals with minimal effort. If any of those players stay active, you have a steady stream of credits. It's not a one-time reward. It's a reward that is usually a little delayed, but can keep earning you credits every month.