Every driver past 314.22 on my 2x670 SLI had a gamma issue or something every boot. My screen would be all washed out. I would have to go touch the Digital Vibrance control to fix it every boot and after every sleep. My monitor was connected via DisplayPort.
I reported this every single time a new driver came out via Nvidia's feedback form as they request with no fix.
I finally tried hooking it up with a DVI cable instead after reading a few posts and that fixed the problem. Sad that Nvidia can't probably support the latest display interface. Even worse is I'll never know if it gets fixed as I'm not going to be swapping cables to test every driver release going forward.
I pwnz j00!