Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in anyway.
A recent project meant that there were errors in the AD settings for users when an account is disabled.
Here are some resources for the issue and links to code the solution
How to find Exchange recipients http://support.microsoft.com/?kbid=251390
THE ADSI RESOURCE KIT IS PROVIDED
http://dev.coadmin.dk/Resources/ADSI%20SDK%205%20HTML/rtk.htm#adssecurity