Money can be used as both a means of exchange and a store of value.
I plan on using Bitcoins as a convenient, very-low-cost means of exchange.
I don't plan on saving a significant number of Bitcoins as a store of value. I like to invest in people who are doing productive things that grow our economy and make the world a better place, so when Bitcoins replace dollars I'll lend them to people by buying bonds or stocks.
If you only use Bitcoins as a means of exchange, then you don't have to worry much about a sudden loss of faith in the system.
If you use Bitcoins as a store of value... well, then you're a currency speculator, which can be highly profitable but is also highly risky. Whether you're hoarding dollars or euros or yen or Bitcoins...