I stood in line on Friday to upgrade to an iPhone 3G. It took about 2.5 hrs to get to the front of the line but the process after that was very easy because I was already an AT&T customer.
By the time I'd left the store, my old iPhone no longer worked as a phone.
The iPhone 3G felt funny at first but I've gotten used to it now. I think actually prefer the feel of it in my hand but it did take a day or two to get to that point. The screen also felt rougher initially but that might have just been some temporary coating and it now feels just as smooth as my old iPhone.
I immediately downloaded Monkey Ball. The accelerometer-based controls are harder to get used to than they looked in the demos. I've also bought the Things app and look forward to when it supports synchronization with the desktop version.
The App Store experience itself was pretty impressive. It is pretty amazing sitting at the airport, deciding you want a new app and buying, downloading, installing and using it right there and then.
The GPS worked nicely in conjunction with Google Maps when my girlfriend and I were going to pick up a pizza last night.
I haven't really done much data stuff over 3G yet as I'm on wireless when at home so can't really comment on how much faster it is. Certainly the signal I get in my apartment isn't any better which is unfortunate.
I haven't played around with the Mobile Me integration yet.
I'll be configuring Exchange support tomorrow at work, so I'll report how that goes.
Overall: the original iPhone was so impressive, getting the new phone was somewhat anti-climactic in comparison. If you don't have an iPhone, the 3G version will be at least as impressive as the original was a year ago. If you do have an iPhone already, the value obviously depends on how important 3G and GPS are to you.