Oooh - just tried it on mine, hold down tab and the start button together and all the pages you have open and showing on the task bar all go 3Dish on the screen. I haven't explained it very well and can't really see why you would want to do it but it does work.
I've messed around a bit more and see I was doing it wrong - you have to hold start and tab then let go of tab and the open windows stay in a 3D way so you can click the one you want ( I was holding both down and the windows were scrolling non stop). Actually I can see that if you have a large no of windows open it could be a way to navigate between them quickly once you've got the hang of it. I will now convert my way of working to be sure to get the most from Vista.
I want to use the 3d flip thingy because I need many windows open at the same time, I do a very techy job (believe it or not!) and have to write long complicated reports on a regualar basis so the flip thing will really help with that.