Yes I have tried dual GPU in a crossfire setup with my x58 board. Crossfire worked perfectly on 2 5770's with a bridge connector however when I tried 2 6770's that dont have the bridge connector I could not enable crossfire. Both cards were detected in Windows but I did not try a monitor on both at the same time (as I was testing crossfire). My aim was to use 2 cards for 2 seperate HTPC machines but then get a decent gaming machine by shutting both down and starting a single VM with the combined resources of both.
The 6770's do work on the same platform when the host is booted straight to Windows so the lack of a bridge connector is not an issue. I beleive its the ATI drivers that will allow crossfire without a bridge only on machines where there are no other GPU's and the VM will always have the VMWare SVGA GPU.