When you think about it, it _would_ be slightly difficult for people who try to run, say, cmd.exe, and have it open as a textfile. If they didn't know how to get to a command prompt *cough*Safe Mode*cough* then things could really be interesting for them.
We had a virus problem at work a few years ago, where the virus assosicated itself with every executable file there was. Problem was, the boss deleted the virus file before telling me about it, so there I am, trying to reset things, without being to get to a command prompt or regedit.