[wetterhorn]

Well, you've covered pretty much all questions, but here is a reply from the builder :)

So does the user sprinkle the powder after each slice, or does the machine somehow do it? How would the machine make an even layer of powder?

The storage bin moves up a little and the build bin down, and then a counter-rotating roller (mounted on the XY-carriage) deposites the powder from one to the other bin.

Why doesn't the powder stick to the print head, or get pushed around unevenly by the print head?

Indeed, the printer head is mounted ±4mm above the powder bed and can never touch the powder. See the printer head moving across the powder bed in this video: http://www.youtube.com/watch?v=bzX5x1A1AMg

Why doesn't the powder fall out during printing?

Because the pistons form a seal and don't let the powder fall through.