Well I havnt had it long, but it was a quick learning curve. Not exactly unused to smart phones so it was only learning a new interface really.
What do I think? Well try taking my iPhone off me and you had better be prepared to die!
Okay a bit over the top but I am entuisastic about it except for a couple of small niggles.

1. My fellow peers (we are a windows/MS house) call me the iGeek now, and keep asking when i am getting an iPad. Well thats easy, not in the future is that likely, it has no place, there is no gap between my iPhone and my Win Based notebook that it can fill!
2. APPs, well Apple are a bit precious here. My HTC had a great wifi analizer that I used for rough and ready site surveys, it was available on iPhone till Apple got precious (giving me a reason why I might want to jail break my phone)
3. Exchange intergration is not so hot, it was better on the HTC, I have to use PUSh if I want folder based email off exchange.
4. The good old minimal multitasking issue, enough said.
5. It cost too much
6. Voicemail button cannot be set by user, has to be set by a carrier pack.
7. The cost of apple accesories which seems to be way over the top

Hell seven negs, or close to negs. But touch a my phone and you die :)

Of course as a newbie to this device I stand ready to be correctted on 1 to 7 above.