I use it because I like Ubuntu, but but want customization options. Ive tried a lot of other DEs but none is easier to use and more customizable than KDE.
the community rocks
I use Kubuntu because it's Ubuntu, but with the awesomeness of KDE. So the familiar technology, coupled with the superior DE means I have never been happier with Linux on my desktop.
I love its pure, unmitigated, raw POWER! It allows me to do more with fewer keystrokes or mouse clicks than ANY other OS available. Dolphin is just an example.
Kubuntu offers a compassionate community, the excellence of KDE and the breadth of the Ubuntu ecosystem.
Kubuntu has a good and familiar look (for those of us coming from Windows), a good base in Ubuntu, and the ease in which to add software and repositories. I also find it cool that both KDE and (K)Ubuntu have 6-month release cycles, meaning a new version of Kubuntu means a new KDE (though a couple months off).