i'm one of the two founders of crowdtilt, in the current yc batch - our modification on the model is crowdfunding for groups of friends (ie instead of a $40,000 documentary it's a $800 party-bus or $500 tailgate), though now it's being used for bigger things like renting out a space for sxsw or renting out a big house for group vacations.

note: crowdtilt doesn't really enter the discussion of this thread, but figured i'd answer your question above