OS X 10.8 Mountain Lion allows for easy password recovery via the Recovery HD partition installed on any 10.8 system. Here is how to reset your password:

1. Boot into the Recovery HD partition by holding Command-R during boot and before the Apple logo appears.
2. After the Recovery boot is complete, Choose Terminal from the Utilities menu.
3. Type “resetpassword” at the Terminal prompt and press return.
4. Choose your system disk (f.e. “Macintosh HD”) and the user account to reset the password for.
5. Enter the new password and hit the Save button.
6. Restart.