Straight to the point...
Layout?I want a 4 player layout that actually allows you to use 4 players at once. Most 4 player tables are actually 2 vertical and 2 player horizontal layout. I want 4 players at once. The cocktail mode works great (it splits a vertical screen in half) so my thought is 2 players on each long end. One potential issue is that if I go with non-orthogonal control layouts, it will make the physical structure, which I will most likely be building from scratch, much more difficult (90 degree angles are always the easiest).
Another interesting concept I came up with is a typical pacman style cabinet with two moveable control setups. They will be USB-plug in and I could either have different places to hang them off of, or have a post they sit on, or both. Here are some of my concepts.

Control Style?Any thoughts on how close the buttons should be to the joystick? I need 8 buttons on each (6 might work, but 8 is best, just to be safe). Think fighting games. It seems that arcade cabinets general have the control right next to the buttons.
Additional Background InfoI have a 21" Sony Trinitron CRT that is going in here. I have an Athlon 64 3200+ that is going in here. I already have 4x ultimarc joy sticks. I will probably use MaLa as a front end (Hyperspin is too much of a hog for this machine, although this machine seems to be able to play any MAME game I try at 100% speed). Games I'm interested in include side scrolling action games (TMNT, Simpsons, Final Fight, Amazing Spider Man), fighting games (MK and SF2), NBA Jam, Gauntlet, and who knows what else!