I saw this amazing shiny shell on the on10.net blog a couple of days ago. A private alpha has just been released to a selected group.
It's nothing like the normal Windows Vista shell, well a bit, it's see though but it's (as I see it) a lot more functional and the taskbar (and start button) is removed. The design is a lot more elegant than the bulky Vista.
This is not just a theme it's a complete replacement of explorer.exe! I collected some screenshots for you to see.

The first screenshot is an example of the explorer concept. As you may see the places bar has been redone as well as the explorer and pictures.

This is the thing I really love! It's so easy to get an overview of your applications, places, system files etc. I am in love...

The last thing I'll point out is the multi-desktop system which is really handy for people with only one monitor, poor them!
The shell will maybe be made for Windows XP as well in the future.
More information and screenshots can be found at http://cairoshell.com/