I think it is fair to say that it is fairly rare. Imagine how many Li-Ion batteries and lights Deal Extreme, Geoman, Shiningbeam, Fenix, Dinotte had sold (and the list goes on). Off course, it only takes one bad reporting to give a bad impression of a product when in reality, there must be hundred or thousand of consumer who had fairly safe usesage of these Hi power batteries.
Personally I think it boils down to consumer education of what hazzard the product carries along with it. This is where the negative reports can be educating and informing and with the Internet available to us, words gets around fast. Sometimes too fast and creates too much fear but good in the sense that it might have prevented something more serious.