If the Magic Mouse right clicking is not working on Mac Lion then you can check whether the feature is enabled under System Preferences.
Step 1 :- Click the Apple icon and select System Preferences from the menu list.
Step 2 :- In the System Preferences window, navigate to Hardware section and click Mouse icon.
Step 3 :- Click the Point & Click tab and mark the check box with label as Secondary click. Make sure to select Check on right side from the drop down list.
By this way you can enable the the right clicking of Magic Mouse on Mac Lion system.