When you say "kicked out" do you mean after the game has started? Or before the game starts and while you are on the list of gamers waiting to start the game (in the lobby) ?
I only ask this because I've had very few problems with this on this demo. Usually if I try to join a game and it says "game was cancelled" or something like that, I think that's what it says after the game has started and I was just too late to join. When this happens, I don't even make it into the lobby and I just have to start a new search for games.
The only other thing I've noticed is that sometimes when in a lobby waiting to play I see gamers names appear for a brief second and then drop off. My guess is that during those games, either the hosts connection speed isn't fast enough to support more than a couple of gamers or perhaps the gamers connection speeds aren't fast enough. I've seen this happen a few times and if it seems to be a problem with the hosts connection, I just drop out and find a different host.
All I can tell you is that my connection speed is only 1.5/3.0 and I've played this demo for literally 8 hours straight with little to no problems.
I've been looking forward to this game all year for the single player campaign, but now seeing how fun the multiplayer mode is, I don't know if I'll ever really play the single player mode much at this point. Either way, I can't wait til this game comes out next month!