I don't want to trivialize the magnitude/scale of the Mt Gox debacle (7%+ of all bitcoin, $0.5B market value, hundreds of thousands of people affected), but the metaphor is that if a bank gets robbed, that wouldn't devalue dollars to 0, and it doesn't make the concept of money a bad idea.
Like cash, bitcoin is susceptible to theft, however there's a whole set of best practices - regular audits, cold wallets that could minimize the risk if you chose to store your coins with a third party (which is currently necessary if you are exchanging/trading coins, however, I'd guess that most of the coins lost by Mt Gox probably shouldn't have been left there in the first place - one of the points of bitcoin is to remove that sort of counterparty risk). If Mt Gox were properly run (as they had previously claimed, with regular audits and 98% of their funds in cold storage) there's no way they could have lost everything like they announced. It's very confusing when/how they lost their coins and hopefully we'll get the actual/real story of what happened sooner rather than later (or never).
Gox's implosion will force exchanges and other coin handlers to be much more transparent (trusted third party audits, cryptographic proof of solvency, at least), but there's no question that bitcoin's susceptibility to theft (both for individuals and institutions) and its dependence on up-to-snuff computer security (which people are horrible at) are big issues, as are the regular-currency notions that money being held by third parties are safer. At least historically, this has not been the case for crypto-coins.
With that being said, here's a sampling of how some other companies that deal with/hold large amounts of crypto-currency secure their coins: