I don't think you understand what "backed" means. A computer, at least not in 2014... maybe in some future "I, Robot" world, cannot "back" a currency. Only an industrialized government with laws, a police/military, and hard financial assets can do that. The U.S. dollar is one of the most favored currencies in the world, even by its enemies, because it's a strong country that isn't going to whither overnight taking its currency with it.
Bitcoin is phoney money, backed by nothing, guaranteed to be accepted by no one. Its value is contrived only by what others are willing to pay for it at any given moment, again, very much like a speculative stock.
I'm saying that its scarcity is what creates its value, more akin to gold than the U.S. dollar. There is a finite amount of bitcoins that can be mined and they require increasingly more power to do so. At this point they are somewhere between a currency and a curiosity, whether they will exceed beyond that will be interesting to see.
I should clarify I am not actually an advocate of bitcoin.