I tried to partition address book by organizational unit using WMI settings with no luck using this guide: http://blogs.technet.com/chlacy/archive/2007/12/04/partition-address-book-by-organizational-unit.aspx

The goal was to have different organizations hosted on the same server, but without them being able to search each other.

I took me some time to find out that the guide missed some final steps. I have here pasted the whole walkthrough and the additional steps are from 17 and forward

UPDATE: For OCS 2007 R2 you need to replace step 4 to 7 with these steps:

• Query
  
• Select * from MSFT_SIPAddressBookSetting where backend = “<Poolserverinstance>”

The original steps fro OCS 2007 R1 is as follow:

1. Click ‘Start’ -> ‘Run’ and type ‘WBEMTEST’
2. Click ‘Connect’
3. Under ‘Namespace’ type ‘root\cimv2’ and click ‘Connect’
4. Click ‘Enum Classes’
5. Click ‘Recursive’ and then ‘OK’
6. Locate MSFT_SIPAddressBookSetting and double-click it
7. Click ‘Instances’
8. Double-click the instance
9. Under ‘Properties’ find ‘PartitionOutputByOU’ and click ‘Edit Property’
10. The default value is FALSE, change this to TRUE
11. Click ‘Save Property’
12. Click ‘Save Object’
13. Click ‘Close’
14. Click ‘Save Object’
15. Click ‘Close’
16. Click ‘Exit’
17. Delete all the files in the addressbook share, server level not client level
18. Open command prompt and navigate to the location to ABServer.exe
19. Run ABServer -regenUR
20. Run ABServer -syncnow
21. Close Communicator, start it and sign in again
22. Then it should work

See this post over at Inside OCS for a complete refence guide about WMI: http://blog.insideocs.com/2009/07/07/ocs-wmi-reference/