So I tried the Stack App and it's pretty slick. You can get the app here:
http://code.google.com/p/mobilestack/
Unfortunately, it appears that you can't customize which apps go on the stack (since it is hard coded), so you're stuck with Terminal, Installer, Maps, Notes and Mail. Still pretty cool though. Can't wait for a fully-functional version of this to come out! Here's a screenshot of it working on my iphone:
