Last December, I had the chance to watch the 12-12-12 Sandy Benefit Concert which featured over a dozen superstar musicians rocking out and raising money to benefit victims of Hurricane Sandy. I was blown away by all these rock stars coming together for such a worthy cause, but something else happened that night: a reunion. Paul McCartney was about halfway through his set list when Dave Grohl, Krist Novoselic and Pat Smear (the surviving members of Nirvana) joined him to play the hardest rock song you will ever hear McCartney play.