Never tried Kubuntu but can see that its really moved fast among Linux users as evidenced on distrowatch.com.
OK, this is a cut & paste of my reply a few weeks ago regarding commercial distros.
I have no problems with anyone wanting to receive monetary compensation for their work. Most distros have volunteers working on them while others such as Mandriva and Redhat are a corporation with a dedicated paid staff of employees.
Now please don't get me wrong, I'm not saying that commercial editions are better or worse then their free counter-parts. The great thing about Linux is that their is a distro for almost everyones differing needs. This is where commercial distros come into play. I would not pay for a distro myself as the free distros suit mine and just about every other home or single user just fine.
Companies and corporations however are not going to dedicate and entire infrastructure to someones "hobby" distro. They want and need the support from companies like Mandriva and want the confidence that they are not going to be abandoned with no support. Commercial distros offer that support and are made specifically with the large business/corporate uses in mind. Without that support and confidence from larger commercial distros Linux will never stand a chance in the corporate world.
So yes, I agree and would not pay for Linux myself as a home user. If I had a business to run however I'm going to want the support that commercial distros offer.
Now for some added thoughts. For the home user wanting an alternative to Windows who is not Linux savvy and wants ease of use then distros such as Linspire, Mandrivas Discovery Packs etc etc are just fine as well. With those commercial home editions that various distros offer they include many drivers and softwares that cannot be included on the free editions. That's great for any user be it beginner or not who does not want to hunt down drivers and programs.
Linspire has given back to the Linux community in the form of code for some of their in house software. At the same time Linspire while having a "click-n-run warehouse" which is a paid subscription to applications also has not gutted APT-GET from Linspire for those knowledgeable enough to use APT-GET for package management.
Commercial distros are good for not only the corporate world but the private sector as well. In time many innovations and features once found only in commercial distros eventually make their way into the open-source community for use in any distro that so chooses. With all the free distros out there people will never run out of choices when it comes to Linux.
