As Sony suffers under the weight of expectation, dismay and an international mainstream media mauling over PSN, Microsoft has issued a warning to users of Xbox Live.
It's Xbox Live status page
has the following warning relating to matchmaking:
"Users may experience difficulties with the following services:
"Users may receive potential fishing attempts via title specific messaging while playing Modern Warfare 2
"We are aware of the problem and are working to resolve the issue. We apologize for any inconvenience this may cause and thank you for your patience."
Xbox Live itself, as well as Markeplace are up and running. There is no warning issued regarding account details.