I upgraded recently to Kubuntu 9.04 "Jaunty", and I made the mistake of installing PulseAudio, the "new generation" audio system for linux. What a mistake. I then spent several hours trying to get sound working again - there is a thread in the Ubuntu forums with more than 125 pages of people complaining about PulseAudio, and this is not counting the whole collection of other threads on the same topic.
Of course, if you want to uninstall PulseAudio, you have to uninstall most of KDE because of dependencies - or so it seems. I had to install first the replacement for PulseAudio (ESound, which works fine, thank you), before being able to purge the pulseaudio related packages. Except one library, which has to stay there apparently.
And now sound works again. Hurrah!