How music similarity measures could be used

Lately I’ve been thinking about the possibilities of songbird (see screencast below), collecting music distributed under common licence or the like from blogs. Wouldn’t it be great to precisely search for music that way? You could say something like “search for music that sounds like what I’m listening to right now”. That means, the method I might be working on should be efficient enough to calculate relevant vectors for different pieces of music fast. Otherwise there would have to be some central service doing some fingerprinting again for all tracks around. But, as said before, that’s not what I’m after. Rather something to get a mutual measure between two tracks, pairwise.

As you can see in the screencast songbird can already, by using diverse search services, find related music. But, as far as I can judge right now, that’s user- or expert-based. That means, the music has to be known well to a certain point to have the data what a newly found song is like. And also it’s text based.