CoD's site writes:
"Since Tuesday’s launch, Modern Warfare 3’s multiplayer has been working great. In fact, the amount of players online is even higher than what it was this time last year for Black Ops. Have fun -- we hope you continue to enjoy MW3 to the fullest.
However, on Call of Duty Elite, we are having trouble scaling the service to meet demand. Many of you are trying to get in and unfortunately, you can’t right now. You’re frustrated, we know it, and we know we need to fix it. Our teams have been working non-stop to identify issues and resolve them as quickly as possible. Again, these issues have no impact on the performance of the game."