Let me preface this by saying I don't have kids.
As a kid, though, I would have LOVED Heelys. I probably would have used them on every smooth surface, even inappropriate ones. Heelys are the new snap bracelet.
I have seen plenty of kids with these shoes, and have never seen them come close to crashing into someone or falling. I do understand parents' concerns about safety, but I don't feel they're as dangerous as regular rollerskates because you can easily stop yourself by just walking. You can't get the speed of an inline skate on these things.
From what limited research I've seen, once you master how to use Heelys and don't try any stupid tricks, like wheeling through a slippery puddle, you're fine.
actually, the BIGGEST safety issue with heelys is that they pose the same dangers as skates or skateboards, but that they are not worn with the same protective equipment (pads and helmets). Parents who would never let their kids on a bike or a skateboard or roller blades without a helmet think nothing of them skating off on heelys b/c they are 'shoes.' Which is how a little boy died in march when he skated into a car on his heelys.
But beyond the safety issues, I just have to reiterate... it's not okay to skate in malls. Or stores. I wouldn't let me kid zoom around the mall on rollerblades, no matter how considerate or careful he is being. Why? Because we DON'T SKATE IN MALLS. just like we don't run in malls, and we don't yell in malls. It's a place to sjop, not a playground, a park, or a skatepark. I don't really have issues with Heelys at the park or around the neighboorhood - provided they are accompanied by the appropriate protective gear. But since my kids have rollerblades and skateboards, they don't need them in those places. Therefore, they are only good for skating in inappropriate places, and IMO... that's just rude.
It's no different than the mom who lets her toddler run around the restaurant. She's not buming into anyone or breaking anything. She's not even yelling, so it should be fine, right? No, because we do not run in restaurants. Simple concept, I thought.
ETA: I would have LOVED them as a kid too, and I would have worn them everywhere. That's why kids have parents to teach them what is okay, and what's not. Kid's just don't always make the best decisions