Poll: Having now seen the movie, I found this dance scene to be:
I voted that the scene was realistic - I thought it was one of the best scenes of the movie. Yet I didn't interpret it as romantic - and that's what made it so fascinating for me.
I noticed that Harry's line "She's like my sister" was not included in the scene after which Ron destroys the locket in the movie. I thought that was an interesting choice as well.