We'll be performing some additional maintenance on some of the Steam servers tomorrow, Thursday, February 28th, 2013 at approximately 16:00 PST (GMT-0800).
Game play for most users should not be interrupted, but Steam chat, game lobbies, matchmaking, and community web features will be unavailable. Content downloads may be temporarily interrupted. Certain multiplayer games that aggressively check for an active Steam connection may also be affected.
As usual, I'll post back on this thread after the maintenance is completed.