These screenshots are from Windows Longhorn build 4029 and are over a month old at this point. I didn't take these myself, and I'm told they leaked to the Web, with annotations, a while back. But these are the originals, and thanks to 1nfin!ty for sending them along.
UPDATE! I've got a new set of Longhorn build 4029 shots available now as well.
So what's new in this build? We can see the same Plex visual style as previous builds, a new design for the sidebar clock, an interesting blend of Aero- and XP-style toolbars, hover-triggered image preview, new WinFS-based visual query filtering, batch image processing, and more.