Ubuntu has been using PulseAudio by default for almost three years. I think that all the nice features PA offers like per-application volume control, audio routing through different sound cards, playing audio over a network, easy configuration of surround sound like 5.1 channels, on-the-fly switching between analog and S/PDIF, Bluetooth audio devices support, etc. are very useful, and sometimes necessary.
That is why I think PA can be part of Kubuntu, like many other KDE-based distributions actually do.
The other problem is that the current mixer information exposed by ALSA is neither user friendly nor useful for everyone. Therefore we also need a Qt/KDE GUI for PulseAudio configuration, like volume managment, etc. (maybe a Plasma widget).