How often do the odds makers "get it right"?

[Phishy McFish]

By "get it right" I don't mean what they are going for (even money on both sides of the line). I mean, is the opening line generally a good indication of what the superior odds makers feel the final score will be in a football game OR is it strictly (or more significantly) related to what they feel the line needs to be to get the public money split down the middle?

My impression was that the opening line was the former and the line movement was attributed to the latter. Am I wrong?