At my current project we experienced the the issue that only one domain controller was listed when trying to configure SharePoint to use a specific domain controller (Shared Services /ssp/admin/_layouts/EditDSServer.aspx?dn=<domain name>).
The specific domain has about 75+ domain controllers world wide, so the fact that SharePoint lists only one is something strange. Because the listed domain controller isn't the closed one, SharePoint will always generate WAN traffic and imports will be slower.
After a long period of troubleshooting we discovered that the Active Directory guys had deleted all _ldap and _kerberos DNS entries (except for the one domain controller) in _tcp.dc._msdcs.
We added the _ldap and _kerberos DNS entries for all domain controller in our 2nd datacenter. We are now able to select the closest domain controller.