Infinity Ward’s “G IH A IN ID II” has given another update via the official MW3 Forums on the current plan to update matchmaking and possibly bring it back to the way it was on previous Modern Warfare games:
“Queued up for release is also a change to the matchmaking system that selects sessions based on the location of the party host as in previous MW games. This means you will need to plan who is hosting the party for the optimum experience. If 5 of your party are on the West Coast and 1 is from the UK make sure you select a West Coast party host. We are planning on messaging this broadly to the community when we release this change.
Sadly the release of planned updates have had to take a backseat while we’ve concentrated on combating the hackers.”
SOURCE: Official MW3 Forums