Though multicore support is now an official option rather than a hidden console command, Valve notes that it is testing the compatibility of the feature, so the option is turned off by default. To enable the option, go to "Options->Video->Advanced" in the game's menu. The brief patch notes follow:
Added Multicore Rendering
- This initial release is aimed at testing compatibility, so the option is OFF by default
- To turn it on, go to the Options->Video->Advanced dialog, and check the "Multicore Rendering" option
- Several performance improvements to decals and client bone/flex setup
- A variety of alt-tab and mode switch fixes
- Improvements to the way the engine initializes surround sound, fixing some specific hardware cases
- Fixed a crash on exit in Vista 64
I can report after just testing for 5 minutes my frames are definetly higher on my q6700.
But I havent played long enough to find out whether its going to cripple me with crashes.