Ken Shirriff's Blogs on this topic have been often cited, and quite interesting. Compares some cheap clones to real (Apple) chargers, and the safety issues. He has several blog articles on chargers, but here is a start:
Ken Shirriff's blog: iPad charger teardown: inside Apple's charger and a risky phony

Ken Shirriff's blog: Tiny, cheap, and dangerous: Inside a (fake) iPhone charger
Ken Shirriff's blog: Apple iPhone charger teardown: quality in a tiny expensive package

IMO, battery chargers for other devices such as lights are another whole wild west. You can never really tell about the quality of these device specific chargers, and the specs are often cloudy if you want a replacement. My original Magicshine charger has some LED indicating a charge/stop charge function, and some units have been known to burn up.

Chargers for specific cells such as 18650 LiIon are a little better if you do research such as on Candlepower Forums.

Danger is certainly there; I decided to never charge batteries when I'm not there. It's amazing to me that more fires and so on aren't seen.