I'm not sure why, but I've been seeing this error a lot recently in blog posts and even news articles. Something about it sets my teeth on edge. I think because the meanings are so completely different, it seems difficult to confuse them. Also, I don't say these two words the same way: loose has a definite "s" consonant and lose has more of a "z" consonant.
I think I also have a sneaking suspicion that the more I see this error, the more likely it is to just become an accepted spelling of lose (much the way judgement became judgment). Somehow this annoys me--I don't think language should remain static but I see no reason for language to change to fit the mental laziness of its users.