I think rectractable leads should come with training tips & rules.

I think if you can use them correctly AND have control over the dog AND use them with common sense in certain areas (not near roads, not in vet offices etc...)

A LOT of people use them & don't know how to control the lead or the dog on the other end. That really irks me.

I use one occasionally, like for hiking & the sorts but I also know how to use one. I know how to real in a dog even if the dog is pulling the opposite way. That rarely happens though because I also have control over my dogs, therefore they don't pull when I don't want them too.

Wolfsoul brought up a good point, I also got a nice gash on my leg from one of those. It was my brothers crazy dog who I had to babysit. That was the only leash they left me. Good thing I had spares at home.
The leashes do have warnings on them (or at least the package) stating that you can get cut, even get a finger or limb amputated!!