kernel bug https://lkml.org/lkml/2014/7/30/548
Attention +Ubuntu users of the +Intel NUC ... If you upgrade to the latest Ubuntu 14.04 Trusty kernel, 3.13.0-32.57, and try to cold boot the system with USB devices attached (a keyboard+mouse in my case), you may render your system unbootable (http://j.mp/1twu9HD).
If this happens, you will probably need to hard power off, hold down the left Shift button while booting to enter Grub, select Advanced boot options, and choose an older kernel.
Huge thanks to the irrepressible +Joseph Salisbury who help me bisect the offending +Linux commit (…