Okay okay... so for all those Windows users with Mac jealousy, now you can have the fancy icon bar with animations too. Check out Rocket Dock. It's free, and it works well.
I don't fit Peter's "Mac jealousy" profile, having had a Mac that I bought for my wife. Neither she nor I were particularly enamored of it, and she ended up requesting that I just give her back a Windows box.
That said, I have tried the second add-in Peter recommends, called Switcher, and it's very cool. It behaves similarly to Expose on the Mac, which is kind of a cross between the Vista Alt-Tab behavior and the new rolodex-style Windows+Tab app switcher.
I think Switcher is most interesting as an example of the kind of thing that's enabled by the new Vista window manager. I think we'll probably see more cool UI widgets and add-ons as more people start playing with the abilities of Vista's Aero UI.