KDE 4.0 was pretty bad. For example, the Plasma desktop which provided things like the taskbar and application launcher menu was rather unstable and liked to crash. On its own, that wouldn't be a problem - it just automatically relaunched after the crash and that was that. Unfortunately, there was another bug where if you set your desktop wallpaper during the first launch (you know, like a new user of KDE 4 probably would) and then Plasma crashed, it would corrupt its own configuration file in such a way that you lost all the things it provided like the task bar and the application launcher, and there was no way to fix this except manually finding and deleting the configuration file because although the existence of the task bar etc was part of the configuration there was no way to actually modify this from the GUI at the time. Made for a pretty terrible new user experience.
