With prior versions of OS X, Apple included a "Reset Password" utility that you could use to reset forgotten passwords for accounts on the system. In the recovery options for OS X Lion, this program is missing from the "Utilities" menu where it used to reside, so people looking to reset their lost passwords may be a bit perplexed as to how to do this. While the program is no longer available through the Utilities menu, it is included on the recovery system and can be used, but you will have to open it by alternative means.
Some people may be thankful that Apple removed this option, because it makes it slightly more difficult to reset passwords on the system. While a reset password will not unlock keychains and other secured items on the system, it will allow access to the system and allow someone to view documents and run programs.
To access the Reset Password utility, you will need to use the Terminal in the Recovery system, so first boot to the recovery partition by holding Command-R at start-up (or by holding Option and selecting "Recovery HD" from the boot menu), and then selecting Terminal from the Utilities menu.
When this is done and a Terminal window is open, simply run the command resetpassword (all lowercase) to launch the Reset Password utility.
The program will launch, but do not close the Terminal window or the program will be killed as well. It is normal to see program output messages show up in the Terminal window when opening programs in this manner, so don't worry if you see a warning or two show up there.
With the Password Reset utility now open, you can select the volume and the account, and change the password for that account.