Mark . is right
Bitcoin will always have usefulness. At the moment its main use is for low cost items - its volatility ensures that expensive things won't find a use for it. But once the price settles down, it will slowly spread bit by bit (pardon the pun) and vendors' confidence in using it for higher value transactions will increase. It has several benefits over "normal" money which make its use attractive.
Think of it as the Poundland of the currency world. Once upon a time Marks and Spencer was a Poundland (okay, in Victorian times they called it a "Penny Bazaar" but same thing).
Mark my words (pardon the second pun)!