Seems like its the opposite for me. I have a PC based mame cabinet. No one suspects its a PC while its running Mame classics. They are surprised when I exit the game and they see the familiar OS.
The nice thing about a PC based cab, is that it is a PC. When mine is parked, it also streams internet radio, plays ripped dvd, works as an internet kioske, and tonnes of other stuff including modern games.
Thanks for everyones advice. I'm going to build another cab and see how it goes. I've got enough parts (old pc, encoder, buttons and joystick) to build another cab for practically nothing.