Yea, it would be impossible in the majority of games to see other clients IPs. Though there are exceptions like the bug in crysis -
http://aluigi.org/adv/crysislog-adv.txt - however, that's just a bug.
It always makes me laugh when people say "that guy has a high ping and it's lagging me... kick him". High ping players do not lag other players, period. If that was the case, I would go into a server and start maxing out my internet connection and lagging the entire server for fun. However, I do agree with kicking high pingers depending upon the game. For example, in some games the players twitch and it may be hard to shoot them. They aren't lagging you, but their twitching makes it annoying to kill them. But in other games their lag is an advantage to you considering you can get a shot off quicker because you see them first ;)