One of my friends just successfully exported 160,000 users from Active Directory for a telecom corporation. He referenced the great solution provided at Microsoft Technet.
http://www.microsoft.com/technet/prodtechnol/windowsserver2003/technologies/directory/activedirectory/stepbystep/adbulk.mspx
Before reading this article, he tried to write script codes by himself. However, to export 160,000 users is not a simple job and he meets errors each time when he runs his own script. Finally he found this article at Microsoft Technet.
“By following the steps in this article, you will not need to write scripts totally by yourself. You could just reference Microsoft's, it's definately safe and good.” He said.
I tried this method on my own Virtual PCs, it worked, so I would like to recommend this article to all IT people who will need to bulk import or export Active Directory objects.