LOS ANGELES (MCT): During the 13 months that Taylor Swift canvassed the globe on her 2011-12 Speak Now tour, she was joined onstage by a steady parade of celebrity musician friends and admirers: Nicki Minaj and Justin Bieber in L.A., Usher in Atlanta, Brooks & Dunn's Ronnie Dunn in her home base of Nashville, Selena Gomez and James Taylor at Madison Square Garden in New York.
On the surface, the guest appearances were simply a bonus for fans -- a little something to generate extra sparks, Twitter and water cooler buzz about those shows.