One quick Vista UI tidbit. Window decorations (titlebars and borders) in Vista are normally translucent. When you maximize a window, its titlebar become opaque. The Vista taskbar is also normally translucent and, like window titlebars, also turns opaque whenever any window is maximized.
Interestingly, this is done even if the window is maximized on another screen. I recently switched from a dark background picture to a nearly white picture, and it's getting frustrating to see my taskbar alternate between black and gray for what seems like no good reason.
Ultimately, this is a small gripe. It's doesn't really get in the way. It's just odd. It reflects a lack of focus on fit and finish at Microsoft. I hope Windows 7 ends up being better.