Several years ago, while being logged into and working on several remote Linux servers simultaneously, I rebooted the wrong one.

I realized it approximately .002 milliseconds after pressing <Enter> (after "shutdown -r now") but it was too late.

Since then, I use one style of prompt on my personal machines and other non-critical hosts. On production/critical machines, I use a different style of prompt that stands out quite a bit and includes the hostname in all caps.

It seems simple (and it is) but it has done the job of keeping me from rebooting a critical production machine during the middle of the day.