Hi spidey647, I am hooked on Survival Mode too. I have waves from 25 to 40's on various maps. My only problems are for some reason: I can't except game invites, I don't seem to be able to invite anyone else to my games. I don't know why? I can add friends.
I have only ever just played public games. That is all I can get to work on my 360. I don't know if I'm doing something wrong in my settings or if someone is just blocking me from joining games for some reason. Anyway I like to play Survival Mode with people who are serious about getting to higher waves. I hardly ever get to play with good players. I always end up teamed with real little kids who are just goofing. Man I hate that lol.