To help celebrate, we’ve upgraded the blog system to WordPress 3.5. The biggest change is the new media manager. It’s easier to use — all you have to do is drag-and-drop your media files onto the popup. It’s especially speedy when you’re making a gallery.
It should also produce better results for you on Retina-level displays, so if you manage your site at all from your iPhone or iPad you’ll have a better experience.
All the details are available here.
Lots of plugins and themes are being updated as well to fully make use of the new features.