I restarted my stock, unrooted, GNEX because it wasn't getting a data connection. When it restarted, it has the Green Android robot and "Downloading... Do not turn off target!!". Some tiny text in the lower left with device specs.
What's the deal? Haven't seen this before that I can recall. It's been stuck like that for 20 minutes.
I took a chance and just pressed the power button. The GNEX rebooted normally and seems to be functioning. Not sure what happened. If anyone knows, I'd still like to hear about it in case it happens again.