Just for fun -this is by all means a reference to Linus Torvalds biography- here's a screenshot of Windows7 with a hacked uxtheme link library. I equipped the mighty Firefox with alpha stage add-ons featuring the upcoming Firefox 4 design.
Hacking the uxtheme.dll and applying the excellent Soft7 theme was easier than I tought and less time consuming than altering Qt4 on Linux KDE4.35.
I modded Firefox 3.6 with Options Fx4 Theme, StrataBuddy 0.6 and SmoothWheel to get MacOSX Snow Leopard-like scroll behaviour. The Icons are Teneo style like seen on the iPhone. I modded Winamp5 with the excellent Ebonite2 skin.
In my opinion Windows7 cutting edge aero engine combined with open source theming solutions (although hacking your beloved Microsoft operating system) gives you one of the best looking Operating Systems I booted these days.