Price and usefulness are two different things. Bitcoin is useful as a good tool of investment or a good asset. But its use as a currency is almost negligible. Bitcoin is not at all a useless thing, its currency of future. Its unique features made it popular so far. But it needs some regulations. Price of any currency is determined by the flow of demand and supply. Bitcoin`s supply is restricted to 21million coins at the time of its introduction. But its demand is growing continuously. This imbalanced demand and supply situation is pushing its price up.