Norwegian TV did a survey on ticket prices OSL-JFK, comparing SK, UA and NAX. SAS came out cheapest 7 out of 10 times, Norwegian only 1. This is after you've added food and baggage allowance to the ticket with Norwegian.
It might take the public a bit to cotton on to the fact there is only 1 ticket on each of the Norwegian flights available at the price they advertise, and that it quickly becomes more expensive than flying a legacy carrier. One can only hope, though, that it won't be too long.