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 usually find it difficult to choose my "best of" for a full year. Sometimes, because I've concentrated on partial high resolution images and shot so few full 360s that it's difficult to find a decent one... Not this year though. This time I shot quite a few and had chosen my one entry for the 2008 Solstice. But... just a few days before the event I did something I hadn't done for a while; a couple of full spherical panoramas at night, with 200 mega-pixels apiece (not that you would notice here). I don't think this one came out too bad, so here it is; my 2008 best of. Let me know what you think!
Latitude: 38° 42' 57.98" N
Longitude: 9° 8' 28.84" W
Precision is: High. Pinpoints the exact spot.