It was behaving strangely under load - worked for a few hours all right, then at some point all 80 cores invariably fell into 1GHz mode with no way to return them to work at normal 3GHz. Probably some software issue, because reboot (and only reboot) fixed it. But after reinstalling multiple kernels and much twiddling, I bailed. Otherwise, a wonderful processor.

I kind of sort of remember reading up on a throttling bug on a laptop that was said to behave like that. I think it was the GPU though.