Thanks for the thoughts. A couple of my own: 1) I'm beginning to suspect a very badly timed GPU start-of-death here. I'm hopefully going to be able to borrow another card this weekend to test. One of my supporting arguments for the dying-card theory is that I booted back into my very old 8.10 32-bit install (which I still have on the system for just-in-case) and the problem is reproducible there (though I never had the problem prior to the upgrade to 64-bit, along with the new mobo and psu I bought at that time since my old psu died and I wasn't happy with the specs of my old mobo). 2) If (1) isn't correct (and, in a way, I'm hoping it is, because I can solve that problem quite easily), then I am wondering if it's a crop-up of an old NVIDIA bug -- trawling forums around the 100.x.x release time, it was commonplace for 7-series nvidia cards to lock up with the proprietary drivers. It would be super-odd if this were the case now for the 173, 180 and 185 (beta, downloaded from <a href="http://nvidia.com">nvidia.com</a>) drivers. I've tried the ancient 96 drivers in the repo, but compiz behaves so badly I can't really even use the machine. I may sound like a spoiled brat, but I need my compiz (: -d