I'm sure regardless of which country we come from we will be aware of loyalty points and club cards. In Tescos (supermarket) we have club points, 1 point for every £1 spent and ever point is worth 1P (1 penny). Anyway.......
At WPMU we get Rep Points, I think it would be awesome if those community members could spend those REP Points, something like:
300 Points = 1 month membership.
Or as a way for you guys to cross promote and up sell:
500 Points = $10 to spend at http://wpplugins.com/
+ Cross promotion of you other site. (Plus upgrades for support and such on WPPlugins, because points would not be permitted to be used for support packages unless they are buying the plugin again
+ Increased customer loyalty.
+ Increased activity in the forums whereby members help support each other and keep the community spirit flowing freely.
What do points make? Prizes! (Sounds like something I recall from a TV game show, not sure which one, lol).