A new look for Ubuntu has long been in the pipelines and is a welcomed addition to Lucid Lynx. The Ayatana Project has done an excellent job at modernising the operating system. I can't help noticing the Mac influence although they've managed to keep the Ubuntu feel. It's a clean, modern and consistent style and in my opinion, it's going to have a huge impact on the perception of Ubuntu. Well done to all involved.
Hardy Heron (Ubuntu 8.04 LTS):
Lucid Lynx (Ubuntu 10.04 LTS):