Well you know any kind of device can be dangerous, or most of them, anyway. See below for some comparisons among wheeled and non-wheeled sports. And while the backlash is beginning for the Heelys, check out the bids they get whenever they're on the skatebay.com most watched ebay skate items list (perhaps visible at the bottom of this page). They seem hot still to me. Much coveted. (Not by me I'll add, but I have not tried them, either!)