most (not all, some contributions are QTVR-only due to historical reasons)
many, but depends on photographer's choice of file upload (newer event = more likely to work) and your device's capabilities. You may experience slow playback, distorted images or unexpected browser quitting if there is only limited memory/GPU power available.
I was shooting a promotional video for Bill McAnally Racing at the King Taco 200 in May 2006. His lead driver, Peyton Sellers in car #16, had a minor accident during the race. It bent the fender which rubbed against the tire causing a blow out that then sent him into a wall that further damaged his car putting him out of the race. Until that point he had led 48 laps out of the 200. That night only one of Bill McAnally's 3 drivers finished the race.
The track at Irwindale, CA is a short half mile track so the racing is brief but exciting. I have shot many Nascar Races in the Southeastern US but I have never shot on such a short track before, it makes for very interesting racing. In the panorama you can't see any of the other cars on the track due to the long exposure needed to shoot this image.
In the Grand National West Division Peyton Sellers finished 7th out of 30 for the season.