Yeah, xylitol is found in the woody cellulose in all sorts of plants. Remember how when we were kids, chewing your greens was a good thing? This is why. When it is industrially extracted (abstracted) and used as an additive, I have grave concerns about (a) its safety and (b) its effectiveness. Declaring it a "natural sweetener" is like declaring saccharin a natural sweetener (it comes from coal tar, natural, right?). Declaring it safe is only a matter of perspective. Aspartame was safe until it was found to be really quite problematic. With over 2.5 million years of human history, to do something in the last few years with even less time out in the wild and be declared safe, it's premature to say the least. Xylitol at least does have a whole bunch of dental positives as well as being sweet.
Still, lesser of a whole bunch of evils - if there's no fluoride in and no aspartame, that's half of the battle won.