I've had this same issue and have dealt with chat, phone, and genius bar support. None of them knew anything about this issue and all tried the same old line of "reset the SMC", despite seeing a trail of support history. I've only had it about a month, and the problems began on day 1. The best I've gotten so far is that when I took it to one Apple store, they sent it off for about a week and it came back with one new graphics card (card B, I believe). It froze the next day. It has been freezing less since then, but the temperature here has been a little cooler, and I could see heat being a contributing factor, though it could just be that one card replaced means 50% fewer crashes. I did educate both geniuses that I visited about this known issue, and the known fix, to which they replied that all they can do is elevate it to be sent off and I get what I get. So I will be taking it in for another try in a few weeks to see if they can fix it.
ps I was able to get into the "graceful shutdown" mode mentioned earlier in this thread by some odd combo of unplugging/replugging the hdmi cable, pressing the power button (but not holding for hard shutdown), and then pressing it again to wake it. As mentioned before, the graphics come back to life but things are slower and it's clear that you have to do a reboot. I don't know if this is related, but shutdown takes a bit longer with this computer than my old mac (any shutdown, not just after freezing).
