Justin Bieber kicked off his Grammy performance on a nostalgic note, with a look at the first time Bieber sang "You Got it Bad" for Usher back in 2007. Fast forward four years later, and the boy who became a teen phenomenon took the stage to strum an acoustic version of "Baby" on his guitar. It only grew from there, as Jaden Smith rapped up a storm and Usher joined in the fun for "O.M.G." We loved seeing these guys show off their moves side by side, but what did you think of the performance? Loving it?