http://forums.steampowered.com/forums/showpost.php?p=25838162&postcount=344
KurtisC (valve):
We are planning to update the Steam servers today, Tuesday October 18, 2011 around 16:30 PDT (GMT-0730). Chat, game lobbies, and the community web site will be affected. Content downloads and game play should not be affected. There's some database maintenance and system updates that we'll be applying, but we'll try to keep downtime as short as possible.
********************
Keep in mind that "game play" means game validation to Steam. The database maintenance will undoubtedly affect SK players because of the way the dependency is setup, and likely continue to knock players off in groups as the steam client gets cut off from the servers. I'll check for any other notifications on the Steam forums and add them to this post if relevant.
I noticed you posted this as a reason for the game logging players out randomly.
Logically it makes sense. But I get these random logouts quite frequently at the moment... like currently (20/10/2011 @ 12:25 GMT) and yesterday (19/10/2011) - somone invites me to a game, i say yes... hit join... then I am there hammering the login button trying to get there in time before the guy thinks I am just ignoring them.
Maybe the maintenance is ongoing? Maybe a mail in game would explaining this might help? First time I have actually been really pissed off with this game :`D trying to play it... and it wont let me :`D
Thank you for posting and helping!