I took some time today to install and take for a spin the latest version of KDE4 today, release 4.3 RC1. I installed the packages from the Kubuntu backports repositories, as explained in this tutorial. All the screenshots were took at 1280x1024 and desktop effects enabled.
The first change it jumps into the eye is the new Plasma appearance, called Aero now. It is brighter than the old one, but I found it looking not so appealing, at least not for the desktop widgets. Here's how the desktop looks in Kubuntu Jaunty, with several widgets running on the desktop: