mrwizzard, the human eye CAN detect more than 60fps, although 60 is regarded as very smooth.
try this: fire up counterstrike (or any half-life game), press ` (the button to the left of "1") then type in "fps_max 30" without the quotes. that will lock the fps to only 30. see how choppy it is? now change it to "fps_max 100". much faster right? try changing it to 60. it will be smooth, but not as smooth as 100.