After the success of the first polymath project (see also here and here as well as the project wiki), there are now two other “polymath” projects going on or proposed. Fields medalist Terry Tao suggested a question from the International Mathematics Olympiad and his blog hosts an ongoing mini-polymath project addressing it. Gil Kalai is meanwhile probing whether there is sufficient interest for a polymath project on the Hirsch conjecture (on which Gil has extensively blogged).
The question of whether to have a “polymath project”, or some other form of collaborative research, related to Algorithmic Game Theory begs itself. The young age of the field as well as the disparate backgrounds involved seem to make it a pretty good candidate for such efforts.