Re: Heff
"all currencies are based on the concept of barter, of a thing _representing another thing_"
Once upon a time that was true. It's not anymore and hasn't been for a very long time. Using the US dollar as an example because it's the one I'm most familiar with, it has been based only on consumer confidence, or 'faith' in the currency, for 40 years now. Despite that, it's one of the most important currencies in the world. Granted that's OPEC's doing, but the cause for the current situation is beside the point. The point is that not only are not all currencies based on something tangible but that some of the ones that aren't are some of the most important in the world.
I'm not suggesting Bitcoin could achieve such a status, mind you. Without the backing of a government its chances of widespread acceptance are pretty slim. It's based on more or less the same thing as the dollar though, which is how well it trades against other currencies. As is the British Pound if I'm not mistaken (though, admittedly, I might be on that point).