Thinner, lighter, made out of glass and aluminum
Bigger, 4-inch screen
For the first time in history, an iPhone is equipped with a display larger than 3.5 inches. The iPhone 5 has a 4-inch screen with resolution of 1136 by 640 pixels, which translates into a pixel density of 326ppi. And the 0.5-inch difference should make a noticeable difference in real life - movies, for example, will look better in widescreen, while a bigger portion of a web page will be rendered while browsing the internet. At the same time, Apple promises that the iPhone 5 will still fit beautifully in your hand, despite the bigger display. Therefore, grabbing the latest iPhone for its larger screen seems justified by the benefits you get from it.
Faster, A6 processor
8MP main camera, front-facing cam with FaceTime in HD
If you are one of those folks who likes taking tons of photos with your iPhone, then you're probably interested in checking out what the iPhone 5 is capable of capturing with its 8-megapixel camera. Well, to be fair, chances are that photos will look about as good as they do when taken with an iPhone 4S, which is why an upgrade is not worth it just because of the camera. If you would like to have clearer, better-looking FaceTime conversations, however, that upgraded front-facing cam should come in handy.
This one is a no-brainer. If you absolutely need to stay connected to the web even when a Wi-Fi hotspot is not available nearby, then it makes sense switching to the iPhone 5, which supports LTE at up to 100Mbps. That's 100 with two zeros! Yeah, that may be just a theoretical peak, but figures in excess of 10Mpbs are likely to be reached under real life conditions, depending on your carrier.