According to Apple's availability page, all U.S. retail stores will now open at 8:00 A.M. every day (except Sundays) to accomodate the heavy demand for the iPhone 3G. They have also started taking a new approach with the handling of iPhone 3G orders. At the start of the day, the stores will now pre-qualify lined up customers and issue them a raincheck that's good until 6:00 P.M. on the same day.
This is a much more efficient method as pre-qualified customers can now come back in their leisure time to complete the purchase. But this also means that people will start lining up even earlier in hopes to obtain one of these rainchecks.
We've been told that the retail stores receive an iPhone shipment every day, so if you are able to wake up early enough, you should finally be able to get your hands on one. If not, you can always try it again the next day.