The Half-Life 2 Fallout Forums were lucky enough to get a quote from Gabe Newell. In this quote Gabe reveals the CS Source dates. Thank you again Xero for the update.
8/11 the Cafe's turn on.
8/16 CZ/ATI users pre-load.
8/18 CZ/ATI turns on.
8/17 Half-Life 2 pre-load starts (textures, audio and other stuff that doesn't change).
News source: HL2 Fallout Forums
