I have roughly a butt-tonne (slightly more than a butt-ton) of USB ports on my "desktop" (tower, ecktually), but I still prefer PS/2, for a few different reasons.
NKRO is one, of course. The fact that my rock-solid Cherry MX-8100 and Alps keyboards are PS/2 is another. (Because I take prednisone, I occasionally lose my temper and pound on my MX-8100 as hard as I can- the keys fly off, but when I pop them back on, it still works just fine. Try that with a M$ keyboard.)
The main reason I like the PS/2, though is that I've never had a port conflict or had the computer just decide to "lose" the keyboard, whereas I've had that happen fairly frequently with USB keyboards (and other devices).
Seriously- what are the advantages of a USB keyboard over a PS/2? (Assuming you have a PS/s port, of course...)