If you can’t get on or stay on XBox Live today, you are not alone. Microsoft’s Major Nelson himself copped to the connectivity issues, stating:
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 disconnected, you should be able to reconnect after a few minutes. Thanks for your patience as we work quickly to solve the issue.
As of this writing, things are still iffy, despite a quick “All clear!” and “Nah, just kidding” from the Major this morning.