I hadn't intended to upgrade to the iPhone 5, but I have done - and I'm not solely responsible! I'm fairly sure anyone with a single iota of interest already knows all about the specs and features, so I'm not going to cover all the reasons why it's a great phone, but I am going to offer a couple of thoughts.
I was extremely skeptical for a long time that the screen size would ever change on the iPhone. Though it eventually became apparent that it was an inevitability I'm fairly happy with the approach Apple took. Despite their marketing hyperbole (see the video below) I always found the 3.5" screen very comfortable to use, and the enormous screens on some Android handsets have always been a deterrent. I don't have particularly enormous man-hands. This said, there are benefits to the extra slice of screen space - particularly for anything that presents you with an interactive list. Twitter, e-mail and the like do well for the additional vertical pixels.
It's also nice to have true-fitting widescreen for videos or YouTube, but I watch so little video that video is probably not a selling point on it's own. The furthest corner of the screen (often where the 'back' button is situated in many apps) is now at the extreme limit of comfortable one handed use; thanks to it being no wider, I can comfortably adjust my grip if I need to. I'll probably have ease of use issues if the screen size were to increase again in the future.
The other noticeable change in the screen is green. The colours on the whole are more vibrant (and accurate) but green in particular looks more vivid. Photos look pretty damned good, and in good lighting the colour representation is actually pretty true to life. Panorama mode is also very cool!
For all the screen's benefits, letterboxed apps that haven't yet been updated officially irritate the heck out of me.
Speed and the Camera
I didn't expect to notice much of a speed/performance improvement. The 4S never felt slow or sluggish at any time. However, everything is very prompt. I imagine the difference would be more pronounced in certain games, but even some simple things like scrolling, and the animations when navigating are quicker and more fluid.
Probably most obviously after a little use is that the camera is much quicker, both in getting from the lock screen to ready-to-shoot, but also between shots.
The camera itself, while physically almost the same as the one on the 4S, takes vastly improved photographs, especially in poor light conditions. This is likely down to the improved silicon and processing. Panorama mode on the 5 also produces significantly better results than it does on the 4S - again likely down to the improved processor.
It's true that if you're used to carrying around an iPhone 4 or 4S this one feels surprisingly light. The spec says it's 20% lighter than the 4S but, possibly due to it being thinner and having more surface area, it feels far lighter. It also is really, very thin. I doubt you could shave more than a couple more millimetres away without having trouble with the headphone jack.
I opted for the white model, after previously (and playfully I might add) teasing that white was the 'hairdresser's iPhone'. There are two reasons: the black model's reputation for enamel chips on the chamfer, but also because for the first time I think the white model actually looks better. I always loved the aluminium backplate on the original, and the bright, clean lines (and the chamfer actually is mirror-like) look really good. The phone is more 'silver', really, than white.
Silver, so say Apple, but it's exactly the same shade of aluminium grey as any unibody Mac.
All in, for an unplanned upgrade I'm pretty damned happy with it. Especially the camera (I ditched my compact camera in favour of the iPhone a couple of years ago, so any improvement is a good one).