Updates to Team Fortress 2, Counter-Strike: Source, Day of Defeat: Source and Half-Life 2: Deathmatch have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:

Source Engine Changes (TF2, DoD:S, HL2:DM)
- Fixed a bug which caused Windows Aero Extensions video option to always be enabled, regardless of setting. Disabling this can improve compatibility with third-party programs and overlays, but may also affect performance.
- Fixed SourceTV showing player counts for the game server instead of the number of clients connected to the SourceTV server

Team Fortress 2
- Australian Christmas has begun!
- Added community-contributed winter event items
- Added new Grordbort Pyro and Engineer item sets
- Added the "Valve Gift Grab 2011 TF2" achievement
- Added Naughty and Nice winter keys to the Mann Co. store
- Added a new Valve-authored control point map: Foundry
- added 12 achievements for Foundry
- added achievement reward milestone reward for Foundry achievement
- Added UGC Highlander medals
- Relaxed some restrictions on what misc items can be equipped simultaneously
- Additional improvements for client stability
- Updated the localization files

Day of Defeat: Source
- Added the "Valve Gift Grab 2011 DoD:S" achievement
- Updated the localization files

Counter-Strike: Source
- Added the "Valve Gift Grab 2011 CS:S" achievement
- Added rate limiting for connections and added the following ConVars to support that:
- sv_max_connects_sec
- sv_max_connects_window
- sv_max_connects_sec_global
- Dramatically improved the dynamic model loading system's memory usage, performance, and stability
- Reduced memory usage on systems running Windows XP, Windows Vista, and Windows 7
- Improved alt-tab handling under Windows Vista and Windows 7
- Fixed a client crash during demo playback
- Updated the localization files