I changed the display setting in bios from PCI to PEG. This seemed to fix standby and boot issues I was having.

I am not using the newer board that you have mine is the GA-P35-DS3P(rev 1.1). Also, I have the E6750 processor. I haven't resolved the issue. Lately it seems to be related to my Nvidia 7600GT graphics card, since it has been doing it on cold boots now too.

I have the exact issue with my DS3P also. I don't ever put it to sleep anymore. I use hibernate instead. I have it overclocked to 3.2 GHz and I am using Gskill Ram at 800Mhz 4-4-4-12 timings. What kind of Ram do you have in it.