Just reported by MSNBC as well. Apparently it was a 777 inbound from ICN. No details on casualties as yet.
ETA: Video of aftermath here:
http://www.youtube.com/watch?v=C1as7d7X2UQ Plane was flight 214 per flightaware.
http://flightaware.com/news/article/...ing-at-SFO/182
The video appears to show the tail section having separated from the aircraft, with the main body of the fuselage intact and not burning. Hopefully there was time to have gotten everyone off safely.