I think of the value of any asset in the form of expected value. For bonds and stocks, it's present value for forecasted future cash flows. For Bitcoins, there

I think of the value of any asset in the form of expected value. For bonds and stocks, it's present value for forecasted future cash flows. For Bitcoins, there is an element of underlying value, but also an element of acceptance as a broader currency. As the probability of Bitcoins becoming a more accepted currency increases, so does it's value. While the underlying currency value may not change (or perhaps it does, hard to tell), its probability of acceptance is going up as Bitcoins enter the mainstream via publicity and mass adoption.