Another partial solution is to up your graphics cards brightness level (which is really brightening the ultimate black level it will output). This denys the cards ability to output really dark colors and makes the terrain easier to see and the contrast between terrain and sky less eye straining.
This isn't quite the same thing as gamma: if you look at the curve, upping the brightness sets a minimum black level that can be generated. Upping the gamma just non-linearly bumps dark stuff, but it can still go to zero (total black).
I have mine set to do both: gamma of 1.9 and brightness (black level) of +50. If you do this, make sure to reduce the contrast setting so that the curve doesn't saturate on the bright side. (Of course one should do this only for the full screen 3D profile, not the normal Windows profile.)