This is an actual demo of a beta of iPhone 4.0. It's in Polish, but there are occasional subtitles to let you know what's being talked about. It was posted last Thursday, and there's no telling how long it will be available on YouTube before Apple asks to have it removed. It gives you a good look at the new persistent wallpaper feature, multitasking, and more.
By the way, I found out about this on Chris Prillo's website. It's worth checking out.