Organize the artwork... There is something that always gets in the way of game development in the open source world, and its the artwork assets. Someone just needs to be on top of this component -- coordinating the art from artists contributions, putting it into the project in a way that makes sense, dealing with the requests from developers to format the art a certain way, etc.

Open Source games usually don't hit the sweet spot until someone does this - alas its not always the sexiest part of the project although, it does become the sexiest part of the project pretty fast, eventually.