Update: All systems are back up and running
Many users have been locked out of their accounts as problems with users inbox's seem to be inaccessible by any means. The problem appears to be system wide, as Microsoft reports on Twitter, stating "@MesaPink The issue will be resolved shortly sorry for the inconveinvce. It is system wide."
Users are unable to access their inbox, as they attempt to login, they are given the error "You don't have an inbox...yet"
Some others users are reporting login problems with logging into Windows Live Messenger, giving them an error "We can't sign you into Windows Live Messenger". As the situation develops, more users are stating problems with more and more Live services.
(Thanks to Shunik Jan for the image)
Link: Discussion Forum