The Minecraft session servers are currently down. No-one can connect until they come back up. http://xpaw.ru/mcstatus/
Ok I've looked into the problem: Servers were down 10 mins ago for 8 mins and then went up for 1 minute then crashed. Minecraft's staff has been having issues with Data bases crashing for a day or 2
Logout just timed out: That means, if you in minecraft, do not get out or you will not be able to get back in. Current: 1.5 mil loggout timed out, 10.5 mil timed out
Looks like it back up, but marked as quite slow. Skins are down now though. Although it seems to be changing a lot, so it might have changed by the time you read this lol