Everyone's speculating about OrigamiProject.com: Scoble, MaryJo, Neowin, News.com... I'm not one to fan the flames or anything... wait a second, of course I am! If the project does indeed refer to the device that Neowin talks about, then we've all seen it before. Microsoft demoed it at WinHEC 2005. While I was there, I had the opportunity to interview a woman on the MobilePC team, where she showed off the prototype device that Bill had onstage. I never published the interview, but I'm going to have to go back through my recording and glean any details I can.. I'll post that later.

(click to enlarge)
I have an extremely reliable source that told me the device pictured above exists for real now, will cost $500, and will be available before the end of the year. It has also be referred to as the "Lifestyle PC", as Engadget has suggested. The reason the screen is so bright is because they slipped a printed piece of paper underneath the screen, so you could see it onstage. At the time, they told me the device was just a very rudimentary prototype; nothing more than a plastic shell. But my sources tell me they were able to get pretty close to this form factor.
Does this remind anyone else of the PADD from Star Trek: The Next Generation and Deep Space Nine? I'm about to show my geeky true colors, but it definitely looks familiar:

SciFi becomes reality once again.
As I've said, I can't confirm that Origami refers to the device they demoed at WinHEC. But as neowin said, it does exist, it will be $500, and it will probably run Vista and be released around the same time.
UPDATE: Neowin has the answer: DigitalKitchen created the advertising spot (Click "Enter", then "Work", then "Brandtheatre"). It looks like Engadget was right. It is important to note that DigitalKitchen did a lot of other work for Microsoft, including the AthensPC Prototype.