I have to say, the music has a richer quality to it, it sounds full, instead of flat, if that makes any sense. I have noticed I want to turn up my XM and "rock out" so to speak. I have not had that feeling in a long time. I also agree with the above comments that there seems to be more noticeable stereo separation with the change.
One question - has this improvement been applied to the Clear Channel commercial music channels, and/or Radio Disney and XMPR? I'm not sure I can tell. The CC cm music channels already use a higher bitrate than the commercial-free XM-produced ones, and XMPR and Disney are two channels that carry quite a bit of music.