Shorting stocks during a bubble is a great way to learn about bounded upside and unbounded downside. I guess in some sense a valuable learning experience is "taking advantage."
EDIT: Let me rephrase. I think it's silly to call Facebook "old and mature" when it IPO'd 18 months ago. It makes it sound like you would have had a shorting strategy for it some time ago, perhaps 18 months ago - which might have failed miserably - but now would sweep that under the rug, pretending to have never had it.
Of course, we can all be clairvoyant if we sweep our losses (FB is up 27% versus IPO opening price) under the rug. Shorting as a strategy works wonders if you ignore when it doesn't.