Yes they are, that was a problem a few years back with the laptop fires. I am not sure if they were not regulated back then or just had a problem with the regulation. They have gotten better, at least you don't hear about any laptop fires on the news anymore (at least I haven't), but that still does not mean they are 100% safe.

You should never charge them unattended, doesn't mean you have to watch them the whole time, but you should at least be in the same area.

I do not mean to scare anyone, many of these batteries are used daily with out incident. You just need to respect them.