We are used to, in Ubuntu, that every release should (and actually does) bring a decent amount of innovation and creativity in fields like user interface, new features, real-estate optimizations, etc.
One quite interesting project that generates much attention and appreciation in Natty Narwhal is "Ayatana Overlay Scrollbars", fancy functional way to get high-quality scrolling, more screen space and a modern UI.
The problem is that, in Ubuntu 11.04, are "heavy" applications that don't use this scrollbars (Firefox, Chromium, etc).