All smart users prefer V-Sync...otherwise the game looks garbage and you will see constant tearing (lag).
I heard some users disable V-Sync because they claim it slows them down. Not exactly true.
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Vsync creates a buffer, which induces input lag. That is quite a proven fact. If you notice it, is mainly based on how quick you personally are and how much the game is limited by the vsync. Underclocking the graphics card can help resolve some of this, and tripple buffering.