This bug cropped up recently in my wife's system using a 7790. The computer would just appear to be frozen sometimes when she shook the mouse or pressed a key to wake the monitor. (This is with the system idling, mind you, and just the monitor in sleep.)
I assumed it was the motherboard dying (an aging Asus P7P55-D that has always been OCed) and ordered a new one from ebay. The video card was fairly new and hadn't had any issues since it was installed in the spring, so I didn't suspect it.
While I was waiting for the mobo, I found information about this Radeon bug. I was pretty annoyed, especially since I wasted my money on a motherboard replacement that I don't need. I guess a recent driver update must have re-introduced the problem.
Bugs like this one and the AMD cursor corruption bug that interfere with daily non-gaming use are the worse kind, IMO. I've sold the 7790 and put a GTS 450 in her computer... of course the lockups have ceased completely. I've always been a bit anti-Nvidia, but AMD may have lost a customer with this one, at least until I find a new reason to be irritated with NV.