Some of my best XBL friends came from randomly meeting them in matchmaking games, back when people actually talked.
Now it's all party chat and silence, good luck communicating if you go in alone because your team are in their closed little group.
It's why I think CGB would be great, it'd bring back the community aspect that has been sorely missing from XBL. If I were to go on Halo:Reach, even during it's peak activity period back in the day, the game still felt...empty.
@Tawpgun - I only intended it for Social Games, I've missed out a lot of points in this thread.