I have a full size 4 player mame, built by Sparky over on MAACA, he did an amazing job on it and it's great.
My only issue is really just one of laziness and feel, certain games (like robotron) just don't have the same feel unless you are playing the actual dedicated machine.
As for laziness, MAME is all well and good, put when you just want a few quick games, I don't feel like having to power on the pc, wait for it to boot, turn on the TV, sound system, boot up hyperspin, browse to the game, wait for it to boot, and then finally get to play.
I'm not good enough at robotron to take the time to do that every time I want to play a game, but like it enough that when I want to play it, just quickly booting up a dedicated machine sounds ideal.
Gravitar is a vector machine so doesn't really work on MAME, but I have a card to create a vector mame, and want to put it in a gravitar cabinet.
Berzerk is for a buddy, he loves the game and wants a dedicated unit, so I'm trying to find one.