Just picked it up at a Verizon store today. I had the iPhone 4, so this is a huge upgrade for me. Here we go:
Design - it really is super thin. But it is the lightness that I simply could not believe. And it's a shame that you can't really experience this in the store for yourself, because of those security lo-jack things. It really is a beautiful device. I had the rep slap it in an Otterbox Defender right away. I don't trust myself! But I did have it out of the case for a while because people at work wanted to check it out. It's funny how the guys all whip out their 4's and 4S's to compare. I have to say, with regard to the extra height, I'm already used to it.
I still don't understand the reasoning for the headphone jack on the bottom.
Performance - if you have an iPhone 4, and use the iPhone 5, you will notice a definite speed increase. Everything is snappier with regard to the OS, and of course the LTE speeds are just insane. The 4G speed is the main reason I got the iPhone 5 today. Honestly, I loved the iPhone 4 - great phone, but it had really only one deficiency.... the download speed. Seriously, if LTE was the only upgrade to the iPhone I would have gotten it anyway.
Apps - I have not had a chance to install any yet!
In conclusion, the iPhone 5 is a worthy upgrade. Some will cry because it looks too much like the 4S. Others will throw a fit about NFC or Widgets. But if you like iOS and enjoy your current iPhone, you are just going to be blown away by the beauty and speed of the 5.