Actually attended:
M Ward droned through an unaccompanied set in open D, because all the songs were in the same key it was getting a little old, until he was ending with a long harmonica jam, which was nice but also running on quite a bit, until the harmonica fell out of the holder. He finished up by scat singing with barely a little skip while he adjusted. He got a standing ovation.
Bono of U2 led the arena in singing Amazing Grace, the wireless box on The Edge's acoustic guitar wasn't working.
Video or whatever:
Too many to mention, honestly.