The idea of "backing" blows people's minds. People feel compelled to locate a persona behind anything and everything. It's human nature.
"But who created the universe" -> Must be a "God"
"But who 'backs' Bitcoin" -> Must be a person, business, physical object (a yellow metal) or gov't entity.
If we had to place a persona behind Bitcoin, we'd probably say that it's "backed" by the people, or the users. A more interesting question would then be "why is it backed by the users?" Reason and Logic, which lead these users to believe that Bitcoin has intrinsic value as a technology.
Both Gold and Bitcoin are backed by the same entity, the free will of the people that choose to use them and the value the people place on them.
Gold is decentralized in the same manner as Bitcoin. If I have a piece of Gold in my possession, that piece of gold is out of the hands of any central system or government and fully in control by myself. Under a Gold currency system, gold is distributed and controlled by the hundreds of millions of people who each possess a piece of gold, not a central government. And it is these hundreds of millions of people who determine the real value of each unit of Gold. Similarly if I own the private keys to some Bitcoins, those Bitcoins are fully controlled by myself and out of the hands of any other entity.
Bitcoin shares more attributes with Gold than I think most people understand, but which will enable Bitcoin to reach some amazing heights. (Provided the network holds and there are no successful attacks)
