My feeling: I suspect Mel Gibson won over more than a few people who were on the fence about whether or not to see The Passion. He came across, I think, as an honest, faithful man, who did what he does best: made a movie, about that which is closest to his heart.
I might add, for all we know about the media’s general hostility to religion, I thought the whole package was quite–overall–fair and, I think, gave enough in terms of images and context to make people want to see the movie—and without handing them a preconceived conclusion (i.e. that it is anti-Semitic, that it is for simpletons, etc.)