Ok, I for one hope that you continue to have a feature where your guest can play splitscreen with you online, however, there are a few concerns with this for Gears of War 2. When I play Gears of War, I am mostly playing with my brother as a guest. We both share a gamertag basically and sort of have to suffer with this. Were Twins and are equally skilled, but when things like linked achievments come in play for multiplayer characters, I would hope you allow the guest to share your multiplayer characters, because my brother likes to be Anthony Carmine.
My next concern is rank and true skill. Now I don't know if playing social matches matter what skill you are, but what will you do with group rankings? Will group rankings be in Social matches? If so will the guest always be rank 1 or however you do this, because that may mess things up, especially when your guest is as good as you.
I know you may bot respond, but it would be nice to know you've even looked at this.