My $PS1 always contains the hostname of the machine I'm SSH'd into IN ALL CAPS so that I never do this (again).
Given the well-established treachery of my finger muscle-memory, I'm much more comfortable with a hard interlock than something that relies on me checking the prompt. Definitely better than nothing though.
I've heard of people doing things like having a terminal background colour escape sequence in their login scripts as well, so it's immediately obvious if you're on a production host.
[1] http://manpages.ubuntu.com/manpages/natty/man8/molly-guard.8...
[2] http://www.catb.org/jargon/html/M/molly-guard.html