Just returned from the con. At the reading, George said that he realized that this decision would be upsetting to some of his readers, but it's really the only option that didn't make him writhe in misery. And the more he worked with it, the more he liked it. Switching between POVs is fun and all, but there's only so many unrelated POVs that a reader can keep track of. This way he gets to put in a lot of the details he was having to leave out (like 3 extra Tyrion chapters), and have books that are more cohesive.
I think it's cool because you will probably be able to ultimately read books 4 and 5 in either order and get the same tale, since they take place over the same time period.
And to sum up George's advice to those who are really, really, really upset by this: Buy both books, take an exacto knife, and dismantle the books into individual chapters. Shuffle.