V-sync or vertical sync, basically when enabled limits your frames per second to the maximun current refresh rate. I always run a high refresh rate in games usually 85hz and dissable v-sync. It should also be dissabled if you are going to benchmark in games like Q3.
On some systems you can get a graphical "textural tearing" with out v-sync enabled but it is usually not a problem if you have a high enough refresh rate.
Damn I LOVE when Bladerunner gets technical!!
Yeah, and here's some more for ya! V-sync:Vertical Synchronization. Also known as the vertical retrace signal. A term referring to the signal that redraws the vertical display of a CRT (Cathode Ray Tube: Traditional monitors contain CRTs, which work by passing an electron beam through a screen filter and onto to a field of phosphorous dots, which light up and define the image you see).
How fast this signal is redrawn is referred to as the refresh rate. Usually given in Hertz (Hz), most videocards synchronize buffer swaps with the refresh rate, so framerates under these circumstances will never go past the refresh rate. Some videocards allow buffer swaps to happen without synching to the refresh rate. This will almost always result in faster framerate results, at the expense of visual quality. When a videocard renders without synching to the refresh rate, visual anomalies, such as tearing and shearing of the image, will occur.
Celeron 533 @ 600
196 Meg. PC 100
Guillemot Prophet GeForce DDR
Aureal 1 Soundboard
19" NEC Multisync Monitor
Hey that made my explaination look very non technical . It is however a much better in depth explaination, but I, ( and I'm sure others), would glaze over if I sounded like a Microshaft sales broucher!!