Valve will be performing some quick maintenance today for Steam, and users may find certain services disrupted as a result.
Well, if you do, don't panic. It's all part of the procedure, as the Steam servers get a little update this afternoon. Valve anticipates that Steam chat, game lobbies, and the community website could be affected during maintenance. Downloads may also be briefly and temporarily interrupted.
On the bright side, you should still be able to play games without problems. Only thing to keep in mind is that multiplayer may be "impacted," but not interrupted.
Maintenance is expected to begin around 4:00 PM PST.