I remember that since Windows 95 or so, I always wanted to find a way to watch a movie on my PC while coding, writing or doing some other work (keeping it "always on top"). Finally, with Vista and its "DWM Desktop Composition" I was able to create a simple application that does simply that: you can clone whatever window is on your screen and watch it in a small thumbnail that always keeps on top of all other windows (even if it hasn't mouse focus).