Valve has sent word that Steam will be undergoing a little downtime this afternoon while planned software maintenance work is carried out.
The downtime's planned from 4-8am Pacific time, which we make to be 12-4pm this afternoon UK time.
"Some Steam services will be offline during this time," Valve said. "Affected services will include the Steam Community, in-game matchmaking or lobbies, downloading games from Steam content servers, and making purchases from the Steam store."
Games that don't rely on Steam matchmaking services should remain playable during the maintenance work.
This weekend Gearbox boss Randy Pitchford called on Microsoft and Valve to fix the incompatibility between titles purchased via Games For Windows and Steam. He claims that the MS versus Steam divide is hurting the PC industry.