I'm not sure, Liquid.
I don't think it was too hard to connect during the Canadian beta, from what I read on GAF at the time. There's a real human host with corny jokes that comments on the game and actual crowd and the "1", so I don't see how they can run parallel games or a game with a thousand people.
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When is Activision? I want some MW2 MP details and I think they hired the dude from The Soup.