-it's not really clear what the on/off button does in the top right
-I think the black bar at the top is ugly, I think you should just leave the social connections on the gray background
-the logos of youtube/musicbrainz look weird on the right, maybe try moving them to the bottom?
-the main box seems to be a little off center
-the name and descrition don't work for youtube videos, as seen here: http://cl.ly/2u1w1v260c1Y2V2k2E34. I assume this is because youtube videos don't have an artist and title. Maybe you could parse it from the title or just make it a little clearer that those fields are empty because it's a youtube video
-what is the value proposition for registering? what do I gain? that's not clear
-where does the "normal search" draw from?
Hopefully those don't come off as too mean, I'm just trying to give some honest feedback.
Nice work overall though! I really like it.
EDIT: Also, skipping forward in a song doesn't seem to work.