Just a quick note – remember to upgrade now! But you knew that already! 🙂
218 people helped fixing the 1217 bugs, with a new default theme called Twenty Ten and a whole lot more.
Matt puts it bets in the release notes:
Theme developers have new APIs that allow them to easily implement custom backgrounds, headers, shortlinks, menus (no more file editing), post types, and taxonomies. (Twenty Ten theme shows all of that off.) Developers and network admins will appreciate the long-awaited merge of MU and WordPress, creating the new multi-site functionality which makes it possible to run one blog or ten million from the same installation. As a user, you will love the new lighter interface, the contextual help on every screen, the 1,217 bug fixes and feature enhancements, bulk updates so you can upgrade 15 plugins at once with a single click, and blah blah blah just watch the video.
And, of course, there’s the video, too 🙂