One picture, of Big Sur in California, caught the eye of Scott Everett from DPreview, the famous photography site, as he was just recently there, and had taken a shot from a similar position, but with his iPhone 4S.
He put the two photos side-by-side for as close a comparison as we can get until the iPhone 5 hits shelves. The iPhone 5 sports a tad nicer colors and more detail, but the lighting that has been in place at the different times might have something to do with that as well, of course.
iPhone 4S photo of Big Sur
Big Sur promo shot with the iPhone 5
What's more interesting is that DPreview speculates the sensor inside of the iPhone 5 must be different than the one in the iPhone 4S, after digging in the EXIF data of the photo. The ISO went all the way down to 50 for this shot, in the case of the newest iPhone, suggesting lower minimum sensitivity than the iPhone 4S, which goes down to 64 ISO at the minimum. Apple claimed that the new and improved iSight camera has been created with low-light photography in mind, too.
Further prodding around the EXIF data yielded the fact that we might have a slightly larger sensor in the iPhone 5 - it uses a 4.1mm lens to achieve 33mm equivalent field of view, whereas the iPhone 4S has a 4.3mm lens, giving the 35mm equivalent.
Furthermore, a reader sent to Gizmodo a similar shot of Big Sur to the ones taken with the iPhone 4S and the iPhone 5, but snapped with his oldie-but-goodie iPhone 4, and its 5MP camera, so you can see the complete three-generational comparison in the collage below.