Update:
I just returned from the Apple Store closest to me, which is not all that close.
I walked in and an Apple employee asked if he could help me, I said sure, but it's probably going to take more people than just you. I then asked if he frequented this site (sadly he said no), so I went over to a new MacBook and pulled up the site and showed him the story on the front page. He found the story interesting, and then I told him that I was the guy that had the laptop, and was interested as to what Apple's stance was on the machine.
He then went to get the manager on duty (the Assistant Store Manager). The manager was with someone at the time so I wandered around a bit and noticed that my initial contact was showing other people the story on MacRumors.
After a bit the Manager came over, and said he was already familiar with the story of the prototype MacBook Air. He told me that I should be alright either keeping it and using it or selling it. I told him that I was concerned about the possibility of it being stolen so he ran the serial number through their internal system and nothing came up.
After that he called Corporate, but had no success getting anyone that could help, but did leave messages. After that we exchanged information and he said he'd be in touch. True to his word he called back within the hour and said he had heard back form Corporate and they did not want the Air back, and I was free to do whatever I would like with it. He said that they would not support it and basically not acknowledge that it exists.
They would, however, not give me a written statement saying this.
I now feel that I have covered myself as far as the legality of selling it, and that is what I now plan on doing.
I plan on taking some more pictures of it and listing it on ebay tonight, and hopefully, I'll eventually be able to get a "normal" MacBook Air.