I'm upgrading from a 3GS. Once I get my iPhone 5, I plan on doing a comparison video I can't wait to experience things like: FaceTime, Siri and overall speed improvements. Also, having "one of the best cameras" on a mobile device will be amazing.
I had the 4, lost it on Sunset Blvd, and have been using a 3G since spring. This is going to be a MAJOR upgrade for me!!! Now if it would only get delivered...