memberships should be by dues

[chadwhitacre]

Right now membership is by simple PR. Dues are completely optional.

We should consider tying membership to dues. We would probably need to extend Gittip to make this happen while still using Gittip, but most naturally we would end up knowing that someone was paying dues without knowing how much exactly.

Why? It puts teeth to membership, for one. And also makes it clear that we're trying to get something economically viable going here.