from what I've read Vsync is bad because it will try to match the frame rate to the refresh rate and if your FPS drops below your refresh rate it chops your framerate in half.
For example, if you run at 1024x768 at 85Hz and your framerate is usually 100 fps, you should be fine. However, if your framerate ever dips below 85 fps (for instance in CS when someone throws a smoke bomb), your video card will drop you to 40 fps and you'll see a little tearing.