Wait, isn't that ... tomorrow? Why yes it is! Turns out that the third week of Mac releases on Steam will include Gordon Freeman's second adventure against the Combine in Half-Life 2. Rather than simply release a press blurb about the game's forthcoming availability, Valve has created this parody of Apple's "1984" advertisement featuring Alyx Vance. It is, much like the original, rather impressive (especially if you're Half-Life dorks like we are).
Valve has not revealed the price for Half-Life 2 for Mac nor confirmed if Episodes 1 &2 will also be made available tomorrow. The PC version of HL2 for Steam is currently priced at $20.