Apparently a fairly widespread disruption in some/all LiveID and Live services has been occuring for a good part of the morning (GMT-8). We don't know more at this point except to say Messenger had issues signing in here, as did Windows Live Mail, and currently although I am logged in to Live ID I can't log out, with a "Service Unavailable" message.
Others are reporting problems as well. We will keep you posted if we hear any official word on the issues, but for now, if you are having problems signing in to and out of the Windows Live services, you're not the only one.
Update: Microsoft has issued a statement acknowledging the issue, according to a number of sources:
"We are aware that some customers may be experiencing difficulty accessing their Windows Live accounts," Microsoft said in an emailed statement. "We're actively investigating the cause and are working to take the appropriate steps to remedy the situation as rapidly as possible."
Update #2: Service appears to be restored, although Microsoft is not saying what caused the problems. Mary Jo Foley has the details.