Command Esc to force quit apps
WOW. Isn't there a network security feature where you can turn that off for client computers? If nothing else, tell them to just stop being idiots. It's not "bad", per se, but it could lead to a loss of data.
Do you have them shut their computers down at the end of the day or just sleep them? And what are you running that takes so long to shut down? Unless it's an in-house application that you can't talk about.