Shiny.
Easy to upgrade, and it looks like there are a lot more features than I am likely to use right away.
50,000 users had grabbed copies as of March 1? Impressive.
It looks good: the default layout (Kubrick) is nice and clean, and the admin interface looks very impressive. I like the Dashboard, with it’s links to pages hosted within the WP development community, as well as the high-level summary of activity.
Looks like a user-focused project . . . like they have really been listening.