Here's Tim Clark's (CEO of Emirates airline) opinion about the 747-8 with some very interesting quotes:
Clark: 777-300ER responsible for sparse 747-8I sales - 2/10/2011 - Flight Global
"What Boeing is up against is not the A380, it is their own machine - the 777-30ER," Clark says.
and
Clark points out that Emirates carries 420 passengers on its 777-300ERs in a two-class configuration. He believes the 747-8I will only be able to carry slightly more passengers.
"Now look at the economics. We can get the ER to operate 17.5h with that kind of payload. It's cheap to operate. The engines are hugely fuel efficient," he says. "You've an amazing capability."