most AT&T stores around me were sold out within the first hour of opening.
Apple stores (I have about 5 near me) didn't seem to run out all day, only that there was a line to get one from open to close of business. Wait times averaged 4 hours or more
(some people that were standing in line were sent home with a voucher to be in the front of the line the next morning)
I just went the following saturday. Showed up an hour before open and there were only 10 people in line. They were already activating a small group of people that were sent home the night prior. Once the store opened at 9am. I was in and out with a white 16gb in less than an hour. When I walked out (almost 10am) the line had grown to several hundred people.