It's a great app, keep up the good work. I really like the logo that disappears when you mouseover it. The spinning CD is gone though! Bummer, I thought that was sweet. Just a couple of suggestions:
More configurable fonts (Font and color in addition to the size). Also, it'd be cool if you could pick the justification of the text (left, center, right).
Make the logo that appears on the right skinnable so we can make our own logos if we want to.
It would be nice if there was a key to skip the currently playing track (sometimes I play an mp3 and just get tired of it). Actually, I just noticed that you had a "Clear Song" button in the last release that did this. Did you get rid of that for simplicity?
Something you might add in the future would be ID3 tag support. You could let the user choose which info is displayed for the song (Some of my mp3 titles are really long or badly titled). ID3 tags would be much cleaner looking.
Good job though, I like it.