It's really creepy to see the ones that are still at Pompeii. There's a group of (casts of) people huddled behind a wall that was between them and the volcano. When we went, the creepiness was escalated by the fact that it was deserted and rainy, and thunder rumbled in the distance. Very sad, but really interesting stuff.
Despite this man's extensive "research" to the contrary, this sort of thing has happened before. Mostly they're made of keratin, and I believe they're called "cutanteous horns of the scalp." Google yields some interesting results.
Though I can see how this might be true, I don't think it applies to all cases. My husband listens to the things I'm excited about and stores away the knowlege to surprise me later. I do the same for him. As a result, gifts are almost always hits. It probably helps, though, that we're both nerds.
I wouldn't mind jewelry made out of one of those shells, though.