Wherever Ubuntu goes, Kubuntu is close behind, as soon as the latest Ubuntu release came out, the KDE version, Kubuntu was available for download too. Unlike many distros, that provide a DVD full of software choices that are great for the experienced user but a mass of confusion for those taking their first steps with Linux, Ubuntu provide only one of each type of software, making sensible choices for you. The alternatives can be added later if you want them, but the standard choices remain core, including the choice of a GNOME desktop. Kubuntu uses the latest available KDE desktop and all the system programs are replaced with KDE equivalents, giving a harmonious desktop.
Apart from the obvious choice of a different desktop, Kubuntu and Ubuntu share the same heart. this means that both are Long Term Support (LTS) releases with three years up security and software updates promised. Both give access to the new UbuntuOne cloud service that automatically synchronises documents, bookmarks and contacts between your computers, wherever they are, by syncing each one with your online account. This is also linked to their music store, so any music you buy is automatically downloaded to each of your computers.
Because Ubuntu and Kubuntu use the same software repositories, all software can be installed on either, Kubuntu is not restricted to KDE software, but it is designed with a consistent KDE interface. All of the improvements and changes to Ubuntu 10.10 apply to Kubuntu 10.10 too, including the new look with the unorthodox, acquired-taste window button positioning.
Ubuntu goodness meets KDE goodness, you can't go wrong!