Ninjaboi asked a good question in the forum on whether we'd be using XNA or MonoGame.
I think the two are fairly interchangeable at this point, so I don't have any personal strong opinions.
I think my vote is MonoGame (3.5 just came out a week or two ago), but if everybody else would rather do XNA then I'm fine with that too.
So I guess this is the place to state your preference.
(I suppose we should maybe open this up to other technologies too. If we get the right mix of people, I could also imagine us having two teams, possibly working on unrelated games, or possibly both making the same game and turning it into a bit of a competition. Perhaps something like Unity could be a viable option in that scenario as well. So if that's where your heart lives, then feel free to speak up and say so.)