It all depends on the game.
Some games feel just fine with 30fps, but others feel choppy at that framerate; this is due to, from what little I know about renderers, the use of GetTickCount() in the renderer. At least, that's the situation with Gamebryo games post-Morrowind.
Skyrim, at 30 fps, feels choppy. Limit the fps to 30 and enable iFPSClamp=30 in the settings file, however, then it feels rather smooth. Same goes for Oblivion, Fallout 3 and New Vegas.
Coincidentally, the last three mentioned games have a mod that replaces the GetTickCount function with Time.GetTime(), thusly removing the choppy experience without the slow-motion slowdown due to syncing the game at a 30fps framerate.
Mount And Blade: Warband feels choppy at 30fps. Mortal Online? Feels fine at 30fps. Divinity: Dragon Commander feels choppy at 30fps. Freespace 2? Feels fine at 30fps. Etc.
I wonder if it would be possibly to somehow create a generic implementation of replacing GetTickCount() with Time.GetTime(); would be swanky if that is what makes these stuttery games become smooth.