Unless there's an errant forum post out there somewhere saying different, Half-Life 2 ought to start preloading intractable assets to Steam owners later today, but in the meantime those on the Counter-Strike: Source beta will be pleased to hear that Valve has cleaned up a few issues dogging the current version.
The update should take hold next time you update Steam, and does all sorts of clever things like preventing multiple terrorists purchasing C4 (yep, that can't be good), fixes problem with spraying logos, and more. You can find a full list of the changes on the Steam news page - including a few changes rolled out late last week while we weren't looking.
The Counter-Strike: Source beta is currently available to owners of Counter-Strike: Condition Zero and the ATI/Half-Life 2 bundle, and to members of Valve's Cyber Café Programme. The full version of the game will ship with Half-Life 2 and as a separate purchase option on Steam - probably in mid-to-late September.