You might be able to call it a speculative (digital) commodity bubble. And there's a possibility for this "commodity" to one day go "poof!" and disappear (gov't regulation, hackers, system failure, etc.) Only time will tell us those things.
But I don't see how you could call it a pyramid scheme.
But I don't see how you could call it a pyramid scheme.
http://en.wikipedia.org/wiki/Pyramid_scheme