In terms of functionality, there's a new panorama mode, that allows picture stitching for multiple images into one larger shot (a whopping 28 megapixels in total) -- it looks like the 4S is getting this function as well, though it's unclear if it'll be via iOS 6 or what.
Using Eyes Free mode, Siri takes hands-free functionality even further and minimizes distractions even more by keeping your iOS device's screen from lighting up.