how reset a mac without the password

I discover today dealing with my gf machine that a easy way to get around a forgotten password passes through booting into Single User Mode and removing a file that tells OS X that the first boot setup has run.

Single User Mode: reboot the computer while pressing and holding the Command and S keys after you hear the startup gong.

mount the volume you need to get into. Most of the time your boot disk and can be mounted as "/" with :

sudo mount -uw /
Remove the file that tells OS X that its already done the setup:

rm -rf /var/db/.AppleSetupDone
Reboot using: reboot

Boot back and it will be  like the first time you boot after install.

ciao alex barchiesi