After installation of Fedora 11 which included migration from KDE3 to KDE4 everything was working fine and all of a sudden all the KDE sound apps stopped working. Anytime a KDE app would try to play a sound it would crash and send a Signal 6 (SIGABRT). I examined the backtrace and alkl I could gather was that the phoneon xine backend was balking somewhere and not playing nice. Only problem is that the xine backend was working fine and I couldn;t see any reason for it to suddenly fail after it had been working fine. But there was nothing I could do to get it to work. So I switched from the xine backend to the "gstreamer-phoneon" backend and all of a sudden it worked. So at least my kde sounds work via gstreamer but I still cannot figure out what the hack happened with xine. The way in which sound is handled in KDE has changed since KDE3 and I am not entirely familiar with the new sound system.
Linux is great but it's still somewhat of a headache when it comes to sound.