Sometimes it didn't work, but it was funny to see how much Link jerked about during cut-scenes when he played it. And the song before the third Silent Realm, Din's Power?, was funny and reminded me of my own harp skills (the lack thereof)
The harp definitely wasn't the strong point of this game. Trying to follow those stupid glowing circles? Overall I didn't have much of a problem with it picking up my movements the major problem I had was how lack luster the melodies felt as you played them and how boring of an instrument it was to play. The only side-quest I didn't finish was the lumpy pumpkin one because if I failed the song I didn't feel the need to go back to it because the song bored me.