I'd like to point your attention to the nice bars telling you how much space you have left. In addition, the most important addition would be those favourite links. They aren't as space consuming as they used to be, and they show up in My Computer too. The same convenience in CommonDialog right there in Explorer! Isn't that great?
Then, we have the Network and Sharing Centre, which I would say speaks for itself.
Then, we have Windows Sidebar. It can be full of stuff and it looks really good.
Then, we have the system tray at the bottom. Notice the small gap between the DAEMON Tools icon and the network icon. Now, the network icon and sound icon stay there without being hidden - permanently. Some of you may find this convenient, and some of you may find them cluttering up space. I'm with the former - I use them pretty often, and having them in the same place all the time is kinda nice.
Stuff in the sidebar tend to look nicer outside the sidebar though. :P
And before I end my really short explanation of why you should upgrade to Windows Vista, here's the new Connect To screen!
(Yes, my screenshots suck. They look a lot better in real life - so give Vista a try. Hopefully within the week, you'll see my new post on Vista, which I assure you, is not about why it rocks.)