Mac OS X Lion provides users with the option for checking the list of software updates installed on the system. This is a useful feature when you are diagnosing some system problems on your Mac and want to see whether any recent updates has caused this problem.
Click the Apple icon and select System Preferences from the menu list.
In the System Preferences window, navigate to the System section and click the Software Update option.
This would launch the Software Update window and on clicking the Installed Software tab will display the list of updates installed. This list would display the name of the software, installation date and the version of the software.