So maybe I'm just weird but my MAME cab has become my all-in-one gaming machine. I hooked up a PS3 controller last week and I've been playing my PC games off of Steam. At the moment I'm playing Darwinia. I also played the hell out of an excellent tower defense game called Defense Grid.
I went overboard and built a powerful PC for the cab earlier this year, so I've been taking advantage of it. It's something you might want to consider if you're thinking about building a MAME cab. I'm also glad that I put a volume knob and headphone jack on the front (need it for games outside of a MAME frontend)