Kotaku has fielded many complaints from PlayStation 3 users that their version of Modern Warfare 2 has been ridden with bugs. Trophies weren't registering. Friends couldn't be invited. Word from Infinity Ward is that a new patch corrects the problems.
From the Twitter feed of IW creative strategist Robert Bowling:
PS3 Status: Patch successful. Trophy Unlocks on PS3 now available in Single Player & Spec Ops. Adding more servers to meet MP demand.
We've got requests in to IW and Activision for more details about bugs PS3 gamers have been reporting. Let us know if the latest patch fixes things.