I am not in the AIB, but I'd say the majority of the tail boom in those piccies looks largely undamaged, save (obviously) the end which looks as though it's been chopped by the MR? Might that explain the 'sudden spinning'..?

Knowing which way the Robinson rotors are spinning and the damages on the tailboom, it looks to me as one of the blades has severed the t/b and the stinger (looks as a clean cut) There is a fairly large dent/buckle on the starboard side right at the front of the t/b, that appears as the tail has been pushed toward the starboard side.
There is also very notably damage on one of the blades on the pictures.

Surely, if this would be the case, then I am in no doubt the rest of the helicopter would start to spin like the witnesses/pax/pilot have stated.

As for what caused it to happen, I'll keep my theory for myself at this stage, and leave it up to the local AIB to conclude.

Sabreliner,

Just do a quick search on any AIB/NTSB site, and see how many 737's that has crashed and ask yourself if you feel "a tad uncomfortable" riding in on?! Obviously, you would argue why the 737 is safe (as there are so many build, and accidents per pax-miles is therefore so great. Can also check the good ol' Cessna 172, and see how many accidents you come up with, same thing. There are a good number of accidents with these Robinsons, that are not related to the machine, ie. flying into powerlines etc. which can happen in any helicopter/fixedwing, but they do tally up towards the type of aircraft which is not a correct picture in my opinion.

It was reported on the news last night that the AIB so far has not found any technical problem with the helicopter.

It was said earlier that virtually all of the helicopter has been recovered from the seabed and is being examined in their facilities.

Preliminary report
 

A preliminary report is out today on this accident. AIB Norways Preliminary report 2010/03P (english version)

The report specifically states that the R44 was over MTOW, nose-heavy and the performance margins for HOGE at 700' were limited. IMHO in extracting the power margin by raising collective, the blades could have overpitched, losing rrpm and resulting in the tail boom chop. Without the tail rotor, the chopper went into LTE with a nose down attitude, accentuated by the forward-loaded CG and lack of tail rotor hub weight. Just a theory, as many Robbies have perished in a similar fashion.

RIP to those on board.

But reading the report there is no statement of a "tail boom chop"...

They were lacking in Power, Heavy, CG out in front, and relatively inexperienced pilot, with fog around, but not in fog at the time of the incident.

Pilot may just have gotten himself too far into the stuff, and not been quick enough to recover when things went pearshaped. HOWEVER, this was only a prelim report, and we have to wait until the final report is out.

Sorry for the loss of life...

H.