Mac OS X Lion gives option to associate Apple ID with user account which facilitates to reset login password incase user forget it, and enables file and screen sharing for another computer. So, through guide below you learn the process to associate Apple ID to user account on OS X Lion.
Associate an Apple ID with your User Account
Click on “Apple” menu > “System Preferences”, and then click “Users & Groups”
Click “Set” button followed by Apple ID, and type your Apple ID and password, and click OK
Note: You must have an Apple ID first to associate it with User Account on Mac.