With all due respect, I do not think multi-signature solves the real problem. The real problem is that Bitcoin transactions are irreversible, so even if we realize within hours that a hack has occurred, we can do nothing about it.
Banks as we knew them did not work this way. Yes, having to wait three days for settlement is absurd, but folks are working to speed that up (to just one day, haha). Yes, the fees add up. But the systems have been developed over a really long time, and they have multiple levels of protection against you losing all your money. In the US that's the FDIC and SIPC, for regular-sized accounts. There will never been a direct equivalent for BTC, precisely because no one's national security is tied to BTC. And most people won't buy deposit insurance at any price higher than the "free" one they get from their government.
Early adopters of Bitcoin spoke fondly of the fact that there are no chargebacks. That's a great way to reduce transaction costs. It's also a great way to make sure that when you get hacked (and you will) you cannot recover.
Compare this to the situation with ACH transfers (the US-only, low-cost "wire transfer" system). Anyone who knows anything about computers would be aghast at the technology comprising that system. The security appears to be pretty lame. Yet people do not lose their savings via ACH. Why? It isn't because ACH transfers are so secure--it's because the banks can undo them, which in turn lowers the incentive for thieves. This is a virtuous cycle, by contrast to Bitcoin's vicious one, and the way it works has nothing to do with technology.