I am building a Raspberry Pi based full size cabinet.
It's all a matter of perspective.
Instead of thinking of the Pi as an inferior PC, try looking at it as a superior xxx-in-1 board.
The only xxx-in-1 board that uses memory cards is the ArcadeSD, which costs $325 and does less than the Raspberry Pi.
If someone started selling a 2270-in-1 board with customizable software, usb ports and HDMI out for $35, people would be snapping them up.
I have mine set up to boot directly into advancemenu, and uses Mame4all with the 0.37b5 rom set.
Navigation is by joystick and buttons, and no keyboard or mouse is necessary.
Shutdown is accomplished by pressing the single (hidden) admin button when in the main menu. Pressing the same button when in a game brings up the options menu.
I'm using a modified version of the PiPlay operating system.
This is distributed as an SD card image, so no knowledge of Linux is needed.
You simply write the image to the SD card, plug it into the Pi, and it will boot into a nice friendly menu of emulators.
http://pimame.org/The reason I modified mine was to remove everything except Mame, as I simply do not understand the desire to play console games with a joystick while standing up.
If there are problems with the emulation in this older version of Mame, they are too subtle for me to notice.