Simply put: 60fps on 60hz display is smoother

[Glide]

Actually it DID force it to 0.
I remember this so long ago.
It forced it to 0 on AMD Cards too (their FlipQueueSize equivalent). In fact, their last windows XP driver version (I think a beta for the 7970) still allowed flip queue size to be set to 0, and it did work. (compared to the default of 3, there was much less input lag at 60hz vsync on in unreal tournament 2004, with supersampling AA, for example, even though you could still feel input lag. 100hz with flip queue size of 0 felt great, though).

That option was removed I'm guessing not long after the first windows 7 drivers.

XP is not Windows 7. I don't believe WDDM allows you to use single-buffered V-Sync at all, so on any system using WDDM a setting of '0' was actually equivalent to the current 'Use the 3D application setting'. It may have been possible on XP and earlier.

[Falkentyne]

What exactly is single buffered vsync, and how does it differ from double buffered? (we already know what Triple buffering is though, two back buffers and a front buffer, to prevent the refresh rate /2 or /N framerate right?).

You said that XP allowed single buffered vsync and that's what prerender limit 0/flip queue size 0 did?

[Glide]

What exactly is single buffered vsync, and how does it differ from double buffered? (we already know what Triple buffering is though, two back buffers and a front buffer, to prevent the refresh rate /2 or /N framerate right?).

You said that XP allowed single buffered vsync and that's what prerender limit 0/flip queue size 0 did?

I may have misspoke there. I was always under the impression that V-Sync required double-buffering, but reading up on this issue suggested that a setting of 1 was "single buffered v-sync" rather than double-buffered

There is an Anandtech article which explains some of this: http://www.anandtech.com/show/2794/2
Though it also suggests that you need double-buffering for V-Sync.

Perhaps someone more knowledgeable on the subject could comment on this.
Regardless, I don't believe it's ever been possible to use anything less than double-buffering with WDDM (Vista onwards) even if the driver previously let you set that to '0'.

[Sparky]

What exactly is single buffered vsync, and how does it differ from double buffered? (we already know what Triple buffering is though, two back buffers and a front buffer, to prevent the refresh rate /2 or /N framerate right?).

You said that XP allowed single buffered vsync and that's what prerender limit 0/flip queue size 0 did?

I may have misspoke there. I was always under the impression that V-Sync required double-buffering, but reading up on this issue suggested that a setting of 1 was "single buffered v-sync" rather than double-buffered

There is an Anandtech article which explains some of this: http://www.anandtech.com/show/2794/2
Though it also suggests that you need double-buffering for V-Sync.

Perhaps someone more knowledgeable on the subject could comment on this.
Regardless, I don't believe it's ever been possible to use anything less than double-buffering with WDDM (Vista onwards) even if the driver previously let you set that to '0'.

double buffering refers to framebuffers, not prerendered frames or flip queue. One of those framebuffers is being sent to the display, the other is having a frame rendered into it by the GPU. With v-sync off, those two buffers switch places whenever the frame finishes. With v-sync on, that buffer swap waits until the frame is done scanning(and stalls the GPU because it doesn't have a buffer to start rendering the next frame in). With triple buffering, the GPU starts working in the spare framebuffer while the completed frame waits on the next refresh cycle.