1. use a track ball, once you get used to it, the precision is amazing!
2. get your refresh rate super high... or use a CRT
3. PS/2 keyboard, because split millisecond reaction time is important when in a knife fight/CQC/Pistol battle with the other guy.
Sort of, ok it's like this, ps/2 sends requests directly to your CPU, no software overhead, it's pure hardware. Usb needs drivers and acts like it's own thing, but because of this is is hot swappable and ps/2 really isn't without a switch or other device to avoid problems. These days the difference between is minimal but it can make a difference in things like star craft, super hard platformers and fps games where speed and reaction times are key.