the cursor is drawn independently from the rest of the desktop. it has 0 input lag at the top of the screen where a scanout starts. its behavior doesnt change whether you turn aero on or off
but it's pretty easy to see the vsync related lag on the windows desktop... just drag an icon around and notice how it lags behind the windows cursor.
if you're wondering how when you drag a winfow around, the window doesnt lag behind the cursor, i believe it's because the nonlaggy cursor dissappears and a new cursor becomes rendered with the rest of the desktop.