I can understand Microsoft not wanting it on Live where it could probably be used to somehow exploit the system and allow cheating and whatnot, and also they'll surely allow more polished user content. That's the problem I've had with mods on the PC, the vast majority are pointless, poorly done, or flatout don't work. There are some that would be good but the creators just kinda give up on them and so they never really go anywhere. Every once in a while there is one that is really good that continues to evolve and get better. I think mods on the PS3 would be all right because if it is messed up you can just reboot the system and not worry about it screwing up things (driver/OS corruption for instance). Of course there will be way too many that just create mods that allow them to cheat and so it'll turn out badly, as then it'll be almost impossibly to find games that aren't cheating.