This is probably old news for most classic Mac collectors, but it's the first I've heard of it: a member of the forums at MacRumors.com bought a MacBook Air "as is" on eBay, and when it showed up, he got something even more valuable than the envelope-filler: a prototype version. As you can see above, there's no "MacBook Air" nameplate under the monitor, and hardware inside is dated to May of 2007, which is way before Apple officially announced the machine.
Apparently someone given an early working version of the notebook has already moved on to the new [REDACTED] that Apple is working on, and has sold off their old prototype of the Air. Very cool -- as I said, collectors know that there are prototypes floating around out there still, but this is the first I've heard of the phenomenon. And I like that it's almost a time capsule back into the beginnings of the product we know now as the Air -- the model name given in the software just says "Mac," so this predates the name we associate with the machine. You wonder what would have happened to a system like this if it hadn't actually gone into production and been released.