Someone asked me what happens when micro-black holes evaporate, and I have no idea, not really knowing anything about the theory of black holes, other than what you learn in a first course in GR. What he was asking was whether the black hole just keeps emitting energy (in the form of Hawking radiation, I presume?) until there is nothing left, or at some point is it light enough that it's no longer a black hole at all, but is just a lump of stuff? My guess was that there is some critical value of the event horizon radius below which it no longer makes sense to talk about something as a black hole anymore, but I don't know what that would be - maybe some kind of effective size of the particle(s) involved? Is this even a meaningful question? I hope so, but I'm a virtual layman when it comes to this stuff.