Don't make it the focus of your app or assume that it is good/unique enough to automatically get you into any school--but definitely include it! It's a relatively unique and interesting thing (though as cc123sb says, don't call attention to the fact that you chose to discontinue it!)
I recommend listing it, and then writing about it in the 'expand on one of your activities' question, as it is quite interesting (unless of course you have some other passion that you've been doing forever and want to write about). I wouldn't write your common app essay about it unless you really can't think of a better topic, in which case it could make an interesting essay. I just don't recommend it being your #1 choice because it is only something you did for a summer and doesn't really reflect as much of your personality than just being an impressive thing you did.