To clarify WHY exactly it is 60 fps and not 30: people say TV is 30 FPS and looks smooth. However, since it is interlaced, you actually see 60 fields per second, AND they are motion blurred. On a computer, 30 fps gives you 30 non-motion-blurred frames. Movies, at motion-blurred 24 FPS are not smooth.
Now why do we need 200fps? here is why. Lets say it is 5 years back, and you bought this cool computer that gets 200 fps in Doom*. People say, why? Now, you play Unreal Tournament, you get 20. Its not even smooth - its on the boundary of playable. Basically, it is stupid to still use an out-dated game like Q3A in benchmarks, since everything can pump out >100fps. More useful numbers would be from Unreal2, for example, which is barely playable on my Tbird 700 + GeForce2 gts, but playable on a 1.4 + gf2GTS
* Doom is actually supposed to be locked at a max of 35fps, but its just an example.