I have no doubt this has been done many times, but I finally finished mine ( thanks in no small part to the various unojoy pages and ShiftIn tutorial )
For my purposes, I added 3 macro buttons that emulate a series of scripted button mashes. There is one particular PS3 game which I make a little side cash with online, and this helps relieve some grinding, monotonous and manual behavior.
I also networked it with an Ethernet shield so I can push instructions to the controller from another machine, and essentially run my scripts from there. The network cable isn't plugged up in the picture obviously. That saves me the small hassle of having to flash and reprogram the Arduino if I want to make a script change; I can just recompile a C++ app on my PC.
So maybe this isn't useful to 99% of hobbyists, but I'm plainly ecstatic to finally use my microcontroller and fledgling electronics knowledge to create a thing I can actually use. Electronics, microcontrollers and 3D printing is FUN, but until today I hadn't a CLUE what I could make that would be of value, not made already, cheaper, in China.
I really enjoy my 3D printer also! The controller is a bit steampunk and awkward, but its really not meant to be played with as much as run my scripts, and allow me to manually take over as required.
So I just wanted to share pretty colors LOL. - Happy to have actually FINISHED something.