I'm currently starting my design on my first cabinet. I'm leaning towards a four player setup with at least 6 buttons per player. I'm toying with the idea of having the buttons moveable so that you can arrange that according to the game you are playing. So far I've come up with a track based system (in theory so far) where you could move the buttons in a 5x5 grid. My basic concept came from that little puzzle game where you had numbered squares (sometimes a picture) and a empty square and the goal being to rearrange the pieces in the correct order. I was assuming I could key each button so that no matter what square they were positioned in it would still be the same keypress. Has anyone toyed with such an idea? Any suggestions or better ways of doing this? I could live with 2 rows of three per player but why?! 
Eric
I have swappable metal panels and it takes a lot of planning/effort to accomplish what you're trying to do.
As well as duplication of effort.
Because of this, I have decided to make a modular panel ala jelloslug, but use standard rackmount parts to do it. This will give both super rigidity and flexibility in width of modules. Also the entire panel will be modular
not just a few sections. So I can take a trackball or spinner, and put it on the left, or move it to the
right, or to the center. Same goes for all the other controls and buttons. This will allow me to
swap out all of the different joysticks and other controls I've been accumulating without having to build an entire panel to use them.
I was wary of doing this because I never thought it could be done and be as solid as my metal panels.
I didn't want to have to worry about stability and this will be just as good I think.
I've got the hardware now and am in the 'building' phase. I'll post some pics when it's done if
anyone is interested. ( If only I had thought of this in the beginning!! )

~brian