I think it's initially startling when you see a character in a movie who doesn't look at all the same as they did in the book, whether it's race or just hair coloring or something, but if the actors are good, they make the roles their own and soon you can't see it any other way.
For example, one of my favorite movies is the Kenneth Branagh version of Much Ado About Nothing, and it was rather alarming to see that the Prince was Denzel Washington -- but of course, it's Denzel Washington, so it wasn't long before it was perfectly his role and nobody else's.
Another one is Ford Prefect -- but again, it was immediately right. It had never occurred to me that Ford Prefect might be black, but apparently he was.
It really bothered me that Draco Malfoy was pale and blond, but when I went back to look in the books, it turned out that he had been that way all along and I had just missed it. So even if you describe something very clearly in your book, some people just won't notice, and will still insist on seeing something different. Or maybe it's just me!
I think if the race of the character doesn't specifically matter to the story, it's not even something to point out -- that way, everybody can see what they want. If it does matter, then the movie should stick to that.