I think it's a fair question. I'm a heavy user of my iPhone 4, and for me it's that for the past year, my 4 has started to show its age -- lagging when using my podcast app, slow camera response, things like that. I'm also eager to try out the improved camera and Siri. So I really can't wait to get my hands on a phone that will be much faster, improved, and with features I don't currently have.
Plus, honestly, I am the kind of geek who's incredibly impatient to get his grubby hands on a new toy, so it cannot get here fast enough. I'm the same way when I'm building a computer and am waiting for the components to arrive.