Ive had mine for just over a month. And I am still very much in love with my Iphone. I literally find out something new to do with it everyday. 3G is great, fast and picture quality is amazing.
Could not recommend the iPhone highly enough.
As for application, my new favourite is PhotoSwap. Completely free, you just take a random photo of where you are, and get a completely random one in return, from someone, anywhere in the world, taken withing 10 seconds of yours.
Sure, you do get a large amount of feet, walls and laps, but I have had car accidents, attractive lady folk drinking beer, a man show me his collection of guitars (you can reply to people who send you a picture, and they can then return to this, apart from that there is no way of getting your number or any information), and a photo of Old Trafford (East Stand) yesterday half an hour before the game started. Extremely addictive - have a go if you have got an iPhone.