In Unity 4.6 and 5.0, when using linear color space, everything is very dark in Rift. It doesn't matter if it's deferred or forward rendering, DX11 or 9. Linear gives just super dark, burnt out image. It's the case for both 0.4.2 and 0.4.3 integration. Oh, and when in linear space, everything looks normal in Scene view and in normal cameras. It's just Oculus, that gives the dark image.
I also suspect what happend - I forgot to install new firmware to the helmet, when upgrading to 0.4.2 and 0.4.3. I don't know if it was this what caused the linear color space dark, but maybe?
After full upgrade to 0.4.4 (including installing 2.12 firmware) it works correctly.