Within Socom you have a friends list (and separate clan list) and so you could follow your friends into a room, you don't have to be invited. While in the lobby (between games), you can choose which side you want to be on. In game, you have the ability to vote out cheaters/obnoxious children.
You can customize a room to have any map/gameplay that you want and you will still gain rank (or xp in COD) BUT the ranking system sucks so rank really means little.
And for the clan part of it. When a clan is created, ONE person creates the clan, gives it a tag AND name and then invites you into the clan. Only if invited can you wear a specific clan's tag. (Theoretically, you can create whatever tag you want but you cannot NAME your clan the same as someone else's. So you can check a player's stats where the clan info. would be located, to see if he/she is legit.)
Stuff like that ...
Wow, that does sound a hell of alot better than COD4 system. Maybe they will improve on that in a future patch.