General:
•Stability improvements to address rare and infrequent hangs
•Implemented a workaround for missing audio issues with certain hardware (SoundBlaster X-Fi, Realtek onboard, etc.)
•Fixed save games being lost or corrupted if connection to Steam is lost or if user switches to offline play
Multiplayer:
•Fixed XP being incorrectly affected by offline play (though only in the local stats; this will be corrected next time you connect to multiplayer)
•Fixed other players sometimes appearing to have the wrong weapon or continuing to fire indefinitely after dying
•Fixed rare issue where players would be temporarily invisible
•Fixed some selection of servers and players in menus sometimes being incorrect
On a related note, you can check the changelog for the AvP PC patch #1 (16/02/2010)
Source le blog rebellion