Anyone wh has been on this forum (especially the video forum) long enough will tell you this crops up every couple of months. here are a couple of points
1 the human eye has a limit in excess of 200 fps
2 tv's use interlacing to double frame rate
3 Tv programs use motion blur to trick the eye into see more frame than their really is
4 producers try not to use panning shots with fast action as these look really bad
5 LCD's dont show up frame rate problems as much as CRT's due to the backlight being on continuous
6 LCD's tend to blur pat their response time - some people dont notice this blurring ala motion blur
7 in a slow RPG game 25fps is acceptable in a fast game it isnt 50-60 is better but remember you will have dips in rate
8 the eye is more sensitive to changes in frame rate than continuous
Their is a little program called frame rate compare ( search google for fpscmp02.zip as original site is down) which allows you to run 2 moving blocks side by side. Running a crt and disabling vsync (having fraps in background to make sure its disabled) allows you to change each one independantly. I guarantee you will notice the difference between 30 and 60 and 75% of people will see the difference between 60 and 120
Edit found it
30 vs 60
When using make sure vsync is off if you want to see above 60hz / fps having fraps in the corner will confirm. Look for the differences around the edges as it moves down and track it with yoour eyes.