The only two suggestions that I have at the current time are:
The ability to refresh the library on the left pane without having to refresh the page, which inevitably stops the music. As when adding music, this can cause some problems.
The ability to list items in your library by ID3 Tags, as organizing by folders (which I really should have done in the first place) is not always done properly (cough me cough). This beats having to go in and re-organize the folder structure.