gavit: a membership class can only have at most one user/account associated to it, right?
Now that I'm thinking it through, jhass may be correct. One user can have multiple memberships, I'm guessing 1 currently active membership, and 'n' past memberships. So many-to-many would work.
Radar: that is often the case, I find. In open source, there are too many changing parts and the agile world, things are too hectic, so heuristics are used to keep up with the fast changing environment. Those biases can also blind us :)