I curently have only 3.
My MAME machine (My pride and joy ):
2 8-way sticks
1 4-way stick
Tron Style Stick
Trackball (Translucent with Superbright LED)
Spinner (Oscar Pro)
Lightgun (Act labs tv version)
Atari Joystick (Wired into player one)
8 Buttons per player
3 Each for trackball and spinner
1 on each side for pinball
Coin 1-2, Player 1-2..
29" TV
AMD Athlon 1.8Ghz (Only really only play the classics so this is perfect)
512MB DDR Ram
Geforce 4 MMX
Soundblaster Audigy
Boots right into a custom Linux distro.
Atari 2600:
I have this wired to my Linux box with an I-Pac. I found a fried one on ebay ($2) a while back and tried to think what I would do with it.. Works like a dream. NO mods to the atari whatsoever save for the joysticks and paddles. This is great when I have people over and everyone wants to play an Atari.
NES:
Again wired into my Linux Box and made from a dead system. Nothing all that special here other then the modified controllers (USB).
So anyway. There's noting like playing on the real thing, but these last two are just the results of being bored. I can't bring myself to hack up an Atari to make one of those portable ones..