When I first got into PC gaming, I remember reading almost everwhere that you only needed 25 FPS for smooth FPS, and a few places claiming that you couldnt see a difference with anything higher
The difference for me is very easy to see when I'm rotating the camera in my RPGs. While an FPS of around 30 doesnt stutter horribly, you can notice a lot of blurring due to frame skipping compared to just 40 FPS which is only 10 higher, or at least I can.
Just about every game I play runs at 40-60 FPS on my setup with everything maxed out, and I wouldnt want any less.
Now, one thing that a lot of people overlook is that the reason why the 'human eye cant see more than 60 fps' is maybe because such comparisons were made on a 60 hz monitor. I surely cant tell any difference over 60 hz, but thats not because of my eyes, that would be because that is the limit of most monitors. 120 hz monitors havnt been around for very long, and have only recently become available in screen sizes of 24" and above, so I doubt that any of the information I read regarding 'Not being able to see the difference above 60 FPS' is in anyway accurate when I really dont think the comparisons were made on a 120 hz screen.