This has never been a concern to me before, as I don't game... but I have in front of me a shiny new WASD keyboard because it seemed to be potentially competitive with Filco (which is what I'd originally planned to buy) and with the 10% discount and custom keycaps it seemed to be worth a shot. So I'm sure that someone is going to ask, "is it really 6KRO over USB and NKRO over PS/2?" I can't answer the second question, not having a PS/2 port, but I'd be willing to test the first if someone could tell me how to do it in a rigorous manner. I'm running Ubuntu 10.04 and also have a Windows Vista partition which is functional but I seldom use.
I did check all the keys through xev and they all check OK... also just by opening up an openoffice document and trying to type and hold random keys down it *appears* to be 6KRO but I obviously was just noodling around and not testing "properly."