A couple of weeks ago I saw some questions about the UR (User Replicator) in OCS. How does the UR replication processes the information from Active Direcotory.
What is the UR (User Replicator)?
OCS user settings are stored in Active Directory. User information and ofcourse global services are stored into ADS and are replicated to the OCS database during the day. The replication process is performed by a OCS component of the OCS service called the UR (User Replicator). The UR service only reads information from ADS and never writes information back in a bi-directional way. The logic of the UR is to contact te closest Global Catalog (GC). Source: OCS Resource Kit
As an addition to the story of Thomas (LCSKid) OCS uses the UR in the same way as LCS2005.
After some investigation into OCS the same MSFT_SIPESGlobalRegistrarSetting object is still there.
How can you edit this object?
UserDomainList attribute of MSFT_SIPESGlobalRegistrarSetting WMI
1. Log on to the computer that is running Communications Server 2007 Standard Edition or Communications Server 2007 Enterprise edition by using an account that is a member of the RTCUniversalServerAdmins group or that has equivalent permissions.
2. Click Start, click Run, type wbemtest, and then click OK.
3. In the Windows Management Instrumentation Tester dialog box, click Connect.
4. In the Connect dialog box, type root\cimv2 in the Namespace box, and then click Connect.
5. In the Windows Management Instrumentation Tester dialog box, click Query.
6. In the Query dialog box, type the following in the Enter Query box according to the edition of Communications Server 2007 that you are using, and then click Apply:
For Communications Server 2007 Enterprise pool
Select * from MSFT_SIPESGlobalRegistrarSetting where backend="server name\\sql instance"
For Communications Server 2007 Standard Edition
Select * from MSFT_SIPESGlobalRegistrarSetting
Data type: string 
A list of distinguished names (DN) of domains that host Live Communications Server users. The user replicator replicates names from all the domains in the list. If the list is empty, the user replicator replicates names from all domains in the forest.
The default is empty.
This property can be updated.
You can also update these WMI settings through powershell. So install Windows PowerShell onto your OCS server.
The companion CD (attached to the OCS Resource Kit book) includes a signed version of the OCS-ALL.ps1 script file. This script file has been digitally signed by Microsoft, and it can be used in environments where the execution
policy is configured as AllSigned. This script is specially designed to script against OCS by Microsoft PowerShell enjoy!