Edit: Jeanphi pointed out something important that I had missed:
jeanphi wrote:Scenes using rough materials (metal, roughglass, ...) should be reexported, the exponent computation has changed wih current development tree (it's approximately the square of the old value). The pool scene I often use for regression testing uses the metal material on the big sphere, and once the roughness is converted it works flawlessly, otherwise numerical inaccuracies when using too high exponents make it appear almost black.
The other nice news is that I've (hopefully) managed to do a SSE1 build of the Qt GUI. In order to cut down on my build directory I'm using the SSE1 build of Qt for both SSE1 and SSE2, again I don't think this should affect performance since we don't use any heavy functions in Qt.