When I was in The Valley last August, I went up to Glacier Point with the express purpose of having my wife shoot a picture of me doing a handstand on this feature. When I got to the overlook there were two hundred people there and about half a dozen rangers, not to mention a railing where it was posted that you were not permitted outside its perimeter. I guess you have to get up pretty early in the morning for that one.
No railings on top of Half Dome, and usually not too many people. I've been where the person is in this photograph, but I've never seen anyone walk out on the diving board.
In may of '07, we climbed the NW face. We hiked the trail and slept at the the base (opted out of the death slabs). I woke to the sound of something ripping through the air. When I looked up, I saw one BASE jumper had already launched and the other was standing on the diving board. Both were flying wingsuits and from exit 'till out of sight I never saw them deploy their chutes!!