According to the Daily Express Pink Floyd is slated to perform at the Olympic closing ceremony on Sunday, August 12th 2012.
According to an unnamed source:
“It’s long been made clear it would take something very special to get Pink Floyd back together again and it doesn’t get any bigger than the Olympics. Like Sir Paul [McCartney, who is tipped to open the Games], they have been a major part of the nation’s culture over the past 40 years and it will be very fitting that they’re involved when London is on show to the world. It’s hoped everything can be confirmed in the coming weeks.”