KDE 4.1, the second major release of KDE 4, has been released. KDE 4.1 adds new applications (including the KDE PIM suite), improvements to the Plasma desktop shell, and improved frameworks for developers.
The same day as KDE 4.1 was released, packages were available for Ubuntu. You can easily install a KDE 4 desktop alongside your normal Ubuntu desktop and switch between both.
Add the KDE 4 repository to Ubuntu: Open System->Administration->Software Sources. Select the Third-Party Software tab. Click Add, and paste in this repository: