keychain information is stored in your home directory I believe, so you couldn't just re-install the OS, it still wouldn't let you into your user account (and thus your data).
A couple of questions:
- have you tried turning it off and on again (yes, I know it's IT Crowd cliche, but you should at least give it a shot)
- did you try waiting a while and then trying your password again? There's probably a 3-strikes lockout mechanism followed by a time-out before you can try again
- do you have another Mac that you can use to access your locked one? If you do, try connecting to it over your network and seeing if you can at least access your files
I did a bit of googling and there are a few reports that this was a bug in 10.8.2, but if you reboot the machine you can get in. It is fixed with the latest update.
Before you do anything drastic, I'd recommend visiting the genius bar at your nearest Apple store.