I'm experiencing poor quality with playing mp3's, m4a's, etc. It does not happen 100% of the time. Usually after a restart if I open nothing but, say, Banshee, music plays fine. But if the computer has been on awhile or a number of programs are started, the music pops and crackles. There are also little digital squawks that sound like what I imagine pixalization would sound like if it could make a sound. (But that might not be a helpful description...) It is true both of music off the hd and streaming.
I have all newest versions of gstreamer, plugins, etc. on Fedora 10.