I didn't buy one yet, but figured I'd post my thoughts here from my experience trying it out (especially in comparison to my current phone, a Treo 650).
But just in the brief period of time I got to spend playing with one of the floor models; wow, is all I can say.
Honestly, the iPhone exceeded the hype for me. It's almost impossible to go back to using my Treo 650 now.
Also, I don't know what they are doing with Safari, but they have managed to make it get a LOT more out of EDGE than my Treo does.
I turned off WiFi on the floor model in order to test out EDGE..... loaded up cnn.com and some other fairly intensive sites. For comparison, cnn.com on my treo 650 takes a few minutes to load up, and frankly, it's almost impossible to navigate it well anyway with the Treo's web browser.
On the iPhone, the cnn.com homepage seemed to load MUCH quicker....... it seems like they are doing a good job of loading up text and displaying it, making it much easier to read while the image elements, etc. on a page load up. My Treo frankly chokes trying to handle all this.
My sole reservation I think had been that EDGE would be too slow for what the iPhone does; but whatever wizardry they're working, it paid off.
Frankly, it loaded up cnn.com quicker and was easier to navigate than any of the 3G phones I tried today at the AT&T store (Blackjack, Treo 750w and Cingular 8525).
And I did try a number of other random sites too, just to make sure it wasn't something simple like the cnn.com homepage being cached.........
Honestly, if all the iPhone was was a mobile web browser, it would be hands down worth it. It just completely blows away IE on Windows Mobile, and Palm's Blazer web browser is just a joke comparitively.
On the Windows Mobile side, even having 3G doesn't do you much good if navigating a full website in Mobile IE is practically impossible.
EDIT: I also have to say, the keyboard was a pleasant surprise. Personally I've never been a huge fan of the Treo 650 keyboard, but it gets the job done. But I was really impressed with the iPhone's virtual keyboard; seemed to do a great job of picking up what I was typing, and rarely needed corrections, etc. I don't miss the idea of a hard keyboard at all.