So minor ones so far that I've heard...
Lead of AWOLNATION surfed throughout the crowd on an actual surfboard
Radiohead slightly changed their set list
Major ones I've heard...
St. Vincent did a few songs with Andrew Bird
Recyclsauraus Rex art was up
John Fogarty showed up to the Black Keys set (thanks IceyHotshot)
Master P made an appearance for A$AP Rocky
Thom Yorke singing with Modeselektor
Usher performing with David Guetta
Anyone else know any that attended both weekends?