Flip Queue Size
 

I noticed this setting in ATI Tray Tools, but I can't find any information as to what it t does. Anyone know what it's supposed to do?

This is the same as "Prerender Limit" or "Max frames Rendered ahead" on the Nvidia cards. It basically tells the driver how many frames (one complete "image" on a screen = 1 frame...if you are getting 60 FPS, you are seeing 60 distinct "images" on the screen per second) ahead it should render into a "queue" before it actually gets output to the screen. Think of it as temporary storage.

This can improve the framerate SOMEWHAT (we're only talking about a few fps), but this has the drawback of causing some pretty bad input (keyboard / mouse) lag, especially when the framerate (when caused by video card bottlenecks, NOT cpu bottlenecks) drops, or when you are using vsync ON with a low refresh rate (again= lower FPS, since with vsync, your refresh rate= FPS (Unless the fps drops).

Setting it to 0 will greatly reduce any mouse lag encountered by a low framerate. I don't know if there are any other benefits of leaving this at default or increasing it (besides the greater chance of input lag at lower framerates).