Justin Bieber, Miley Cyrus perform together; New York still standing

justin-bieber-boyz-ii-men.jpgNow we know why Justin Bieber briefly encouraged fans to storm Madison Square Garden on Tuesday: His show featured a boatload of special guests.

The MSG show was filmed for the 3-D concert movie/biopic Jon Chu ("Step Up 3-D") is directing, and as befits a big-screen extravaganza, it featured a lot of cameos. Justin's mentors Usher and Ludacris were there, and so was Sean Kingston. Boyz II Men -- whose biggest albums were released before Bieber was born -- got in on the act as well (that's them above with Justin).