I also had the similar situations where I was getting close to finish the process. Definitely it is not broken but if Apple can improve so that when you are at the last mile, at least the server allows you to keep the session till the end for a limited time. The most time-consuming part of the experience is even when you are on the very last stage of the order process, the server busy message can blow you off and waste all the efforts.
Finally able to secure one iPhone 4S tonight.. looks like the 2nd batch of stock just came in in Toronto area as the store I reserved actually had everything in stock regardless of colour and size when I made the attempt tonight. This is the 1st time I've ever seen a store with complete inventory since I tried 2 weeks ago.
Let's hope I get a good one tomorrow without problems as I think it is difficult to get it replaced due to stock quantity..