It seems frightening to me as well but I've noticed on several of my friends' hubs as well. I've been spending some time hanging out with friends here and there helping each other figure out how to fix stuff on each others' bikes, and basically anytime I've tried to put a back wheel back onto my or any of my friends' bikes, I've noticed the hub wobbling. I remember looking through old threads to see if there were anything already posted about it on here, and the consensus seemed to be that hubs wobble because there are so many components and there is a slight margin of error in how each of them fits together, so there is naturally some degree of wobble. But I can just as easily believe that hub wobble is something that shouldn't be happening