Supposedly mw3 got a patch where they essentially removed lag comp in tdm. Don't think they ever did it for any other game mode, but they certainly could have. Hold onto your game, you may end up losing 5-10 bucks in trade in value holding it for a bit but at least give them a chance to try fixing stuff.
Von said they won't make any big patches for a few more days to a week, still collecting data or something.
"Persistence until excellence." http://www.youtube.com/user/supercoolisaac