Also of interest...
In Active Directory Users & Computers, enable the "Advanced Features" option on the View menu. Then, when examining the properties of a user object, click on the Attribute Editor tab. This tab contains a list of every attribute, either mandatory or optional, that is capable of having a value or list of values assigned to it. For the attributes that do have values, the values are displayed; otherwise, the text "<not set>" is displayed in place of a value.