Noticeable Choppiness but stable FPS

Another obvious question is what refresh rate is your monitor set at?

My lcd is 60Hz, so my frame rate at 60 with vbl sync keeps the screen memory updates in perfect sync with the monitor display. (I actually have my fps set a little higher but the vbl sync will cap it at 60, the monitor refresh...note it is possible to forcibly disable the reporting of the vbl to applications in your gfx card settings)

However, if your monitor refresh is 75 or 80Hz for example, and you set your target fps to 60 then it will look choppy, even with vbl sync on.

even at 60/60 refresh / fps rates, it is still noticeably choppy. But I believe this to be an issue with video cards, especially ATI.