I've had that happen since PR1.0, with stock kernel. There's a small bug in the SGX driver in the kernel that in just the right scenario, will cause it to spin. In PR1.0 and stock kernel it can be triggered by having a couple of apps constantly updating their display, even when in the background. (Modrana and a couple widgets used to do this, which is how I found out about it.)

There are patches to the SGX driver upstream, but they haven't been back-ported to this kernel. I know Titan was looking into doing so, and some of it may have been ported back since you still had enough interface to reset the device. In stock and Titan, when sgx driver went south the display froze and you were done... if you were lucky a long power press would shut you down.