I like the idea. And I also use winamp advanced controls with the keyboard. And I also never change windows volume, unless there's no other way, like in the webpage example.
As a sidenote, it would be nice if there was a way to control the volume of the web browser, because often the flash videos or sounds coming from webpages have no volume control, which is really annoying. it would be cool if firefox or ie had it's own volume control, like in the status bar area or something.