When I see the "Xbox live down" keywords in our access log files hitting an old Xbox Live update story, I know that some Xbox users cannot access the Microsoft online platform.

Update 12/31/07:
Xbox Live still having problems

It is now Sunday, one day before Christmas at 2am EST and the Xbox Live support page states that: "Users may experience intermittent issues when attempting to connect to Xbox Live. Our engineers are continuing to investigate and are working to resolve this issue. We apologize for any inconvenience."
Considering the amount of queries we are getting, this does not seem to be a system wide issue and only a portion of users are having problems connecting to Xbox Live.

So you can only hope that the Microsoft Support people who drew the "I have to work Xmas card" will fix it by tomorrow.
Via the Xbox Live site.