I've already per-ordered mine but, I think the 4S was a bigger jump over the 4 than the 5 is over the 4S. 5 to 8 megapixel camera, dual antenna, 7x faster graphics A5, image stabilization, SIRI, louder speaker. The 5 has a bigger screen but other than that, everything else is less obvious.
Plus, I even think the 4S is a better looking phone. It has pleasing proportions and the glass back with chrome apple is still sexy. The 5 looks oddly long and the two tone back reminds me of a car with body panels that don't match.
I'm getting the 5 for one reason, to try the longer screen. I just hope it's not too big to take to the gym. My 4S is a nice iPod substitute at its unobtrusive size. You never see big android phones at the gym but you see a ton of iphones strapped to peoples arms. If the 5 wasn't lighter, I would have hung on to my 4s another year.
The best case scenario for me would have been a 4 inch screen with no increase in length.