Extensive guides,videos,etc can easily be found on how to build a MAME cabinet. There were even a few episodes devoted to it back on Revision3's Systm. I built one of my own a few years back using a salvaged Galaga cabinet and various PC parts. I loved recreating the arcade feel ... I even wired the power switch to the coin door so that you need a quarter to turn it on. However, this is a huge and heavy beast.
I've been wanting to make a smaller, mobile version that can easily plug into anything from a home theater to a crappy SDTV. I would like to see an all-in-one solution housed in a 2-player joystick enclosure. Imagine just dropping that on a coffee table in front of the couch and only having to run a power cable and A/V cable to the TV. Also, some easily accessible USB ports would be nice for some of those 3-6 player games.
I'm thinking maybe something like just mounting the motherboard/components directly inside the joystick ... or even just going with something like the Asus eeeBox. Maybe there's a better solution, but I hope my basic idea is clear.
Thanks and love the show so far