Video actually runs at 60Hz (NTSC) on TV sets, because the picture is interlaced. One frame shows half of the scanlines, then the next frame shows the other half. This method effectively doubles the refresh rate of the video.
Anything below 60 on a computer monitor is definately noticable. This is probably due to the way CRT monitors work. LCD screens are better at showing low frame rates because they only refresh the pixels when needed. There’s a reason why film looks good at only 24fps, but I can’t remember the reason.
High frame rate is essential for some gamers, as performance is paramount in games such as first person shooters. One slight slowdown or jitter on your computer can often mean the difference between winning and loosing a shootout.
Basically games play a lot better with high framerates! There’s nothing like stuttering along at a low frame rate to break the immersion of a game. It can get frustrating trying to do things when everything isn’t running smoothly.