Well don’t fear as you are not alone. Major Nelson writes in
In the past few hours, the Xbox Operations Center noticed that large number of members were disconnected from Xbox LIVE, some more than once. Our Engineering teams are actively working to determine the root cause of this issue and to prevent it from happening again. If you are disconneced, you should be able to reconnect after a few minutes. Thanks for your patience as we work quickly to solve the issue.
Do you think it might have to do with the 10,000 people that got access to the New Xbox Experience yesterday? I think so too, and while 10,000 people might sound like a lot, that is less then 1% of the people that actually have Xbox 360. So if this is an issue now, just wait till the 19th when the NXE is open to everyone.