I did my research, surfed the net, read the blogs, and called a couple of AT&T stores to gauge the stock of iPhones. Did my homework and confirmed by phone and internet that I was upgrade eligble. Also realized that Apple stores would be crazy busy and not able to fix any AT&T issues, and decided not to go to an Apple store.
Went to my local (Largo, FL) AT&T store at 4:30am, 7 people in line ahead. Knew this was a good thing, as my research suggested that each store was going to get about 20-40 iPhones. Had a great time with people in line, well worth the wait, lots of kidding around and joking. We even moved two chairs near the front back to the end of the line, these guys were in their A/C car while all of us were sweating in line. Somebody bought egg mcmuffins for all of us, and I had my 2G iPhone and a DVD player to pass the time. The line at 8pm was about 50 people, somebody didn't do their homework!
AT&T staff were great, went through the line at 7:30am, getting info about our upgrade eligibility and which iPhone we wanted. Very professional. Surprisingly, a lot of people ahead of me wanted a white iPhone, but good for me, I wanted a black 16gb. Went inside at 8pm, they had about 7 service reps to process everything. Activation did lock up, but after about 45 minutes all was cool, I had my iPhone 3G. They even traded out my iPhone for another one when I noticed a dented microphone mesh cover.
Everybody was cool and calm, great experience overall and much smoother than I expected. For such a great platform and high demand/expectations, Apple and AT&T overall did a great job, just to give another opinion.