well i played with a friend the coop mode on my XBOX with xbox live.
But then we've got disconnected all the time and I don't know why???
And it's just in the coop mode thats happen.
Some of the people say that's with the sensibility of your mic, you know when you talk too laught.
I'ts funny because all my orther games like Halo 2, ghost recon work fine on xbox live.