People that have touted the PS/2 version over USB have made that argument mostly based on using a hardware keycaster to control multiple computers.

Personally, I use a USB version through a USB-based hardware keycaster and have had very few problems. There have been a few times when I am spazzing out and mashing a ton of buttons that some keys don't get turned "off" but this is rare.

They do make some PS/2 to USB convertors, but you have to be careful because some of them (i.e. the cheaper ones) supposedly don't necessarily transmit the proper keycodes.