Nice work! The UI is simple and focussed on the music, feels fast and responsive.
One thing I can't easily tell, though, it why you built it. It was obviously a lot of effort; what feature was YouTube missing that made the effort worthwhile?
I really enjoy the creativity and the insight that goes behind applications such as this where you can't immediately tell "why?"- Might not sound like it makes any sense, but at first sight I really couldn't tell you "why" I have had this running in a tab since I saw this link.
It's beautiful. It grabs exactly what I want. It works, and it works quickly, with minimal effort. I wouldn't say that it fixes any one problem that I have had, rather it makes one of my life's conveniences a little better. That is cool, and I think this industry could make large impacts thinking the same way.
One thing I can't easily tell, though, it why you built it. It was obviously a lot of effort; what feature was YouTube missing that made the effort worthwhile?