If you set the gamma slider in the graphics settings, then alt-tab to the desktop, then come back into the game, the game's gamma adjust will appear back at 1.0 (even though if you go back into the graphics settings, the slider is still at whatever you set it to).
This makes it very inconvenient to use alt-tab to hop out and into the game (unless you are using gamma adjust of 1.0 -- and the new terrain lighting is so dark, I think everyone is going to need gamma adjust much higher than 1.0).