As this product isn't out yet for the iPhone 4, I can only speak from prior experience with Power Support films for earlier models. The Crystal film is a glossy, clear film that's meant to protect the screen from scratches. It does, however, get oily from finger swipes and prints. The Anti-Glare film has a matte finish, and will do what the name suggests -- cut down on glare -- as well as reduce fingerprints. The Anti-Glare film does occasionally get cloudy from touch. Both films are easily cleaned and very durable.
I've used both films on my original iPhone, and while its a great product, I wonder if it's a bit too obsessive. The iPhone glass is very resistant to scratches, and oleophobic against fingerprints. These films are also a bit pricey for what you get (2 films per package).
The Power Support films go on the face of the phone (excluding the button and bezel), and not on the back or all over. I thought Power Support made a full body film set, but I may be mistaken. In any event, there are several companies that make full body films, like ZAGG invisible shield. I can't comment on these, and you should check out the iPhone Accessories sub-forum for reviews or suggestions.
Hope this helps.