When you click the Office button in Office 2007, you will see a list of recently used files.
To keep a file in the list indefinitely, click on the pin to the right of the filename. It will turn green and the file will remain on the list until you click on its pin again.
If you are using Office 2010 and do not have a file open, clicking on the File tab, will show a list of recently used files and folders. If you already have a file open, click the File tab, then click Recent to see the list. To keep a file or folder in the list indefinitely, click on the pin to the right of it.
This saves time in locating files and folders.