Update: We have planned the WordPress 3.3.1 upgrade for the morning of Tuesday, January 24, so that the students finishing up fall semester coursework on the system are not distracted by the new interface.
WordPress 3.3 saw its final release on Monday, December 12. WordPress upgrades are usually somewhat painless, but we will be delaying the upgrade of our multisite network for a few weeks. This will give us time to test compatibility with the 75+ third-party plugins on the network. We will also update our quickstart guide. Look for the update after the holidays, the first week of January.
In the meantime, WPCandy has a great rundown of the new features, "Everything we know about the newly released WordPress 3.3." Check out the new admin bar (now called the Toolbar), welcome screen, flyout Dashboard menus, feature pointers, and the brand new drag-and-drop media uploader.
Also, if you first log into lynda.princeton.edu with your Princeton netID, the WordPress 3 Essential Training course has added a chapter to the Introduction, “Differences in the WordPress 3.3 interface.”