I would be mad about this if I had some attachment to the character just because I can be a nitpicky fanboy who likes things to be as close to the source material as possible. That's the only reason to be bothered by this casting (if you're going to be bothered at all) as far as I'm concerned. Regardless, as others have said, I agree it doesn't matter as long as the actor gives a good performance. It's like when Michael Clarke Duncan was cast as Kingpin. I didn't like it at first because I was used to Kingpin as a white character in the Spider-Man cartoons, but he played the role nicely, so I got over my fanboy irritation.
I also think it's a little ridiculous to get so worked up for lack of fidelity to the source material over such a small role. I mean if Hollywood remade Blade or Shaft with a white actor in the lead, I could understand being annoyed, but this is a relatively minor character in the world of Thor, isn't it? Also, I've only ever seen Elba act in his guest spots on "The Office" U.S. and he was excellent there, so based on that I expect him to do fine in the role.
I also think it's a little ridiculous to get so worked up for lack of fidelity to the source material over such a small role. I mean if Hollywood remade Blade or Shaft with a white actor in the lead, I could understand being annoyed, but this is a relatively minor character in the world of Thor, isn't it? Also, I've only ever seen Elba act in his guest spots on "The Office" U.S. and he was excellent there, so based on that I expect him to do fine in the role.