Nothing's fundamentally or structurally changed in the US economy. There were no bad mortgages. We hit the brakes for a bit, but before you know it we'll be back up on our feet and working our asses off, and if we're lucky, we'll get some mandatory paid sick days added to employment law out of it.
[edit] well actually, something has fundamentally changed: the cost of borrowing got somehow even lower meaning an eventual recovery may be turbocharged. The Fed is very unlikely to raise rates as we move past this.