I'll take a bite. A currency that is backed by a powerful and stable state.
A state that enforces nearly constant but low inflation; a process by which money has to be invested and flow into an economic system in order to have a shot keeping the same value.
I bought 7BTC in April-May 2011 when they were at 7EUR each, during one of the first press-coverage booms. Private key is currently in a cupboard on my old laptop; And precisely because Bitcoin has not inflation, they're staying there.