As part of the "New Xbox Experience," as Microsoft is calling it, the company has made it possible to view downloadable content in terms of user popularity.
It's not as robust or scientific as the Nintendo Channel and MTV Multiplayer doesn't know how long it's been tracking these statistics, but it does provide some insight into gamer habits.
So, what are the top five downloads for gamers who are playing "Rock Band 2," "Guitar Hero: World Tour," "BioShock," "Halo 3? and "Gears of War"?