Re, USB limit: A hard, consistent eight-keystroke limit really isn't that bad as long as you stick to single player. Take a skilled keyboard player who will probably hit three of the arrow keys at once (due to a lot of directional shifting and what-not) - that leaves up to five action keys that can be pressed - all by the five fingers on the player's left hand. My main beef is that the key combinations that cause ghosting are _inconsistent_ between keyboards. Most keyboards support holding Z + X + C at the same time - mine stupidly does not (and this is supposed to be a "gaming" keyboard too).

The consequence of this inconsistency is coming up with a sane default keyboard mapping that will work across keyboards.