I'm a long time Linux advocate and user (since around '98). I rarely boot up Windows, but when I do, it's secretly frustrating to me how fast things seem to be. For example, when you type in Ubuntu (after typing in Windows), there seems to me to be a very slight but perceptible lag between key press and character appearance. This also seems to be true in window rendering (minimize/maximize) and so on.
The end result is that the Windows 7 desktop experience seems more performant and zippy compared to Ubuntu 11.x or 12.04 (I've comparison-tested both).
As a fan of Ubuntu and Linux, this bothers me. Is this lag caused by the extra layer that X windows brings? Is this what Wayland aims to address? Or, is it something else?