An update to the Counter-Strike: Source beta and Steam client has just been released. Steam will update itself automatically when you restart. Here is a list of the changes:

COUNTER-STRIKE: SOURCE BETA CHANGES / ADDITIONS:
Improved server changelevel behavior
Improved behavior of full servers
Improved " say" behavior on servers
Addressed SetMode() issues
Addressed " Invalid property: DT_BaseAnimating" issues
Can now create windowed modes at the same size as the desktop
Changed sv_pausable default to 0
Improved command line parsing
Improved change team binding
Improved centerprint ID behavior
Disallowed command " overview_mode" if not in observer mode

STEAM CLIENT CHANGES / ADDITIONS:

Improved pending subscription behavior
Improved ´reusing credit card´ warning during purchase
Changed credit card expiration year selection to go up to 2014
Improved display of " not enough disk space" message in game install wizard
Improved purchase wizard timeout behavior

Source: http://www.steampowered.com/forums/showthread.php?s=4a6390d93db034012b102a013e3b87e8&threadid=125652