Wider interface, more methods of exploring things - map, trendfollowing - more emphasis on your multiple blogs, directory of things you liked, sitewide search, "theme garden" for everybody to upload themes.
Tumblr is sick, unreal and sexy as hell.
Thx. That made me laugh. :) He clearly needs to tone down the bravado a bit in the voiceover, but I admit that it does look slick.