Google could be able to include advanced searching functionality into such a site, making it extremely useful. Imagine, for instance, the ability to hum a few chords of a song you just heard on the radio, but don't know the name of or the singer. They could find the song, or at least potential matches, and offer them up for sale.

That alone could give them a massive edge over Apple, Sony, and other online music retailers. It is a very difficult task to do well, but it may be within Google's reach, considering all the talent they have working for them.