Well, I never paid attention until now - MAME turns off the keyboard LED's when you start a game that doesn't use them. Bummer, anyone know if it's difficult to change the source code so that it turns the LED's on instead?
I may have to choose between having the lights always on, or only on for supported games. Unfortunately I don't think I have any supported games in the ROM set I'll be using on the cab. It's a one joystick with two button machine, so I wasn't even planning on Centipede (trackball), Tempest (spinner), etc...