I like the idea that I can join as many different fellowships that I can (with no restrictions). Lets say there is a limit of 5, you are in 5 now, and as the site grows, there are new fellowships you want to join - well you would have to quit one fellowship which you like to join the new fellowship.
The limit should be that you can only join 1 team out of all the fellowships for each game type. So for example, in Fellowship #1 - I could join the Backgammon team (but could not join another Backgammon team in any other Fellowship) Someone told me this restriction is already in place, but I have never tested it to see.
As a side suggestion - how about letting un-paid pawns join 1 Fellowship. It would let them know how they work, and might get a few of them to join.