Reports of 2 fatalities at this time (per Airliners.net). The other 290-something souls had a very near miss with the Grim Reaper from those pictures.
Listening to the ATC recordings, there was no indication of anything abnormal on the landing at all - no pan or mayday situation, no priority landing, etc. Amazing how fast the ATC cleared the inbound traffic too - and all kinds of interesting diversions for the heavies. E.g. first ever A380 into Oakland.
Total speculation - but it looks like a destabilized approach at the end of a long flight, low and slow and trying to make the threshold. Looks like the gear and tail impacted the bay wall on the runway threshold, rupturing the fuselage just aft of the pressure bulkhead (you can see the intact bulkhead in the crash photos on AvHerald.com). You can only imagine the violence of the pitch down momentum with no tail and no undercarriage.
Surprised that the firefighters could not prevent the fire taking out the whole top of the fuselage - but if all the passengers were off, maybe it was an abundance of caution for the safety of the fire crews?
RIP for the lost souls.