Mac OS X: Hey, where's my admin user?

Hiding an admin user is a fairly straight forward task in Mac OS X.  To do so, open Terminal and run the following command:

defaults write /Library/Preferences/ Hide500Users -bool YES

Now, what if you sit down at a machine and you don’t see an expected admin user?  Well, use that same command with a NO at the end to (hopefully) bring it back:

defaults write /Library/Preferences/ Hide500Users -bool NO