I don't think it's a hiker vs. mtn biker issue, I think it's an issue of personality - easy going people tend to get along better regardless of what they're doing - the uptight will find an issue with something no matter where they go. I've encountered very few problems while hiking or riding, but when mtn biking I've noticed a definite age correlation among those who disapprove of it(not that I'm that young anymore). I suppose one would be more inclined to disapprove of mtn biking if one had been hiking the trails years before mtn bikes came along.