There was quite a lot of buzz about it during Haswell release. Since I was an early adopter
I had no time to check it properly. Now I can confirm that my PSU - Corsair CX430M - is definetly not compatible. I kept C6 and C7 enabled for over a month. During that time I experienced random segfaults in various apps, from intel video driver and OpenGL apps (most often), through compiler errors up to kernel panic (most rare - only 2 times - but each time with partition corruption). I also noticed that most errors happened right after cold boot (yes, I turn off my machine when I'm not using it) and most times they vanished after two or three reboots. After disabling C6/C7 everything runs smooth and stable. I know that these states are designed for laptop battery run times but I'm curious if there will be any difference in electricity bill with them enabled/disabled on a desktop machine.