Heely's has responded to a recent study claiming Heelys WILL KILL YOUR CHILD. They now say, "Okay, they can hurt people but other stuff is way worse." The company which makes Heelys hired Heiden Authorities, a risk assessment company, to analyze the CPSC's numbers. The data confirms that wheeled shoes are still the safest among "popular wheeled sports" and also points out accidents involving wheeled shoes have actually decreased in the last 15 months.
Heelys are, according to Heiden's analysis of the CPSC numbers, 39 times safer than bicycles, 24 times safer than skateboards, 9 times safer than scooters and 7 times safer than inline skates. My own personal analysis of the data found that Heelys are 53 times more annoying than any other wheeled activity, except unicycling which is around 57 times more annoying.
Use at your own risk.