Well in the case of BTConly enugh people have t trust in the usability of it then it could be used to save money. Which is beautiful. But i would assume we also need a cryptomoney that is designed for to be spend - Like many lokal currencys with demurrage http://www.digplanet.com/wiki/Demurrage_%28currency%29 or the brakteaten money in medieval times 12-15 century http://p2pfoundation.net/Brakteaten_Money.