Well, from the recent Xbox 360 brochure that is leaked on the front page, they mentioned that there is co-op via XBL for Perfect Dark Zero.
Anyone think there will be co-op system-link mode? It's great playing co-op over live, sure, but I love playing co-op right next to someone on two TVs (and I don't think two xboxes can sign onto live with one router because of port conflicts).
An interesting question that I want to bring up, since Xbox 360 is so Live based, do you think they will exclude system-link modes in a lot of titles?