Tried it yesterday and liked it. Despite almost every bit of their graphics stack having crashed while I tried that out and looking far from finished (no way to configure the thing how do I change color, add a virtual desktop?), I guess that's what "aplha" means.
Liked it a lot.
It is indeed fast and beautiful. Ubuntu's theme itself does a pretty good job of not distracting you (e.g. no overly colorful icons in notifivation area) and unity's hiding launch bar and collapsing menus and title bars remove more garbage from the screen.