PDC is for developers and Microsoft is building an awesome platform for us developers to exploit for the next 10 - 15 years. Presentation, communications, tools, you name it, we will have it. However, if you think from the end user's perspective, from what I can recollect you would only see a couple of things in the actual look and feel.
sidebar
First page of the document on thumbnails
3D flipping between apps
and app preview on the taskbar
Glass effect on windows, I however have noticed that when you have many windows open the text on Glass is not clearly visible, hope MS does something about that.
I may have missed a few items but you get the message.
The way Kam Vedbrat was showing the video behind the start bar, I hope he was meaning to show the power of the engine and not the actual UI.
I am hoping that with beta 2 we would see a lot of visual enhancements to the UI.