Kurt has just installed Kubuntu Edgy on his laptop to replace Mandriva, so that gave me a chance to compare Kubuntu to Ubuntu.
I have Ubuntu on my laptop now, an almost identical model to his.

Having seen both Ubuntu and Kubuntu, I definitely prefer Ubuntu at this point. Read on for details.

Kubuntu seemed to take longer to load, for starters.

In just a brief session of using Kubuntu, I ran into a number of problems. The first was getting an error when running administrator applications. It would report "Conversation with su failed". What the heck? In the terminal, the result would that the prompt would come back, but nothing would happen. Something seemed broken.

It turned out to an issue of very poor communication. What needed to be conveyed was "Only administrators can run this command, and you are not one." I've filed a bug report about this.

Since I like Ubuntu's "network-manager-gnome" for eady network management, I installed "Knetworkmanager", (except I expected it to be named "network-manager-kde!). However, it didn't seem to work as well as the Gnome counterpart. Although the wireless hardware was nearly identical and recognized, it just wouldn't connect properly with the wireless access point, although the process is automatic in Ubuntu. I'm not certain this was a KDE/Kubuntu problem, but it's not clear what else the difference could have been.

Next, the Adept "Add/Remove" software install tool crashed quickly and repeatedly. Kurt left before I could collect enough useful information to file a bug report. I was disappointed with how few applications were available through this tool. The Ubuntu Add/Remove tool has many more.

Finally, I found the Adept repository tool to be much less user-friendly than Ubuntu's "Software Sources" tool. In Ubuntu, the "universe" repository has an easy description: "Community maintained open source software". A simple checkbox enables it. In Kubuntu's tool, it's a lot like reading the raw configuration file, you see "deb-src", the full URL of the repository, and other unnecessary stuff.

In the time I spent with Kubuntu, I found no features it offered that Ubuntu lacked.

Even though I've been been a satisfied KDE user on Mandriva for users, I'm sticking with Ubuntu and Gnome for now.