So we have upgraded from Exchange 2003 to 2007 a few months back and noticed that we would have user mailboxes or room mailboxes fall out of the address lists randomly (we thought randomly.) BUT.... today, after touching/changing almost every user mailbox in the Exchange console, we noticed that everyone of those users disappeared from the address list in Outlook. In order to get these users to pop back in to the address list, I run either of the following Powershell commands: Get-AddressList | Update-AddressList or update-globaladdresslist -identity "NAMEOFglobal address list-" and whala, the users appear again to the address lists. It's great that I know what is causing them to disappear, but how can I stop it from happening? Could the addresslist commands be scripted to run periodically throughout the day somehow? Any help would be greatly appreciated!!!!!

Have you tried turning up diagnostic logging of the OAL generation process and checking the application log of the OAL generating server? I am assuming it's during the automated process that people dissapear on you.