Got my 2 windforce 670's in.
Not done an awful lot of playing around, but they certainly do perform well in BF3.
Not so much in Heaven, but I don't play that often.
Colours seem a bit dull compared to ATI, which have been using for years now.
Top card runs at either 1137 or 1156 (or something like that), and temps get into mid 70's
Bottom card goes up to 1170 and seems to keep under 70. May swap them around some time if I can be bothered, but I am not even concerned about overclocking them.
I may have a quick go just to get an idea of what they can achieve, but they are more than likely fast enough, even at 2560x1440.
PS - memory usage 1.9GB - should I be worried?