Down also. What's funny is that only LEGIT players suffer when this happens. Offline servers never have any problems when mojang services go down.. It's almost like we have to suffer just cause we bought the game. I think they need a new way of protecting systems cause it doesn't prevent piracy one bit and only effects the people who pay money.
The session server is down, meaning you get an error when attempting to join a server. Once your in a server you don't rely on the session server. That said, if you were in a server already (before the session server went down) you can still play there. But if you attempt to login to the server again you'll get the error.