I had not expected the most expensive SB to sell out first. I had been to Best Buy on Oct 7 & 12 to try and see one in person, but they only had the SP4 demo unit. But at least I finally got lucky online. Now it's only a brief wait.Welcome to the forum and congrats!
I've experienced that on other sites for other products and it is so frustrating because finally you get the process started and you think you are in the process of placing and then completing your order, but then you are told that the item is not available! Arrrgggghhh!!!
I'm sure times have changed since the release of the original SP, but I can tell you that I was amongst those waiting at Best Buy and that experience was a nightmare! I ended up visiting several Best Buys but eventually it was all to no avail and ended up placing the order at the MS Online Store.
On October 6th and 7th, I read enough reviews and comments such that I had enough information and was confident in placing my pre-order for the SB. Based on what I read, I knew that there would be sold-out issues, so I made sure I got my pre-order in fast and early.