I have a customer that's asked about OCS Global settings and whether to install in the system container of the root domain or in configuration partition. Reasons for setting objects into configuration partition include:
limited access to the root domain
distributed domain architecture
empty root domain structure.
I'll do a shameless plug and point out one of my colleagues blog entries on this: http://communicationsserverteam.com/archive/2008/04/18/152.aspx. His entry includes a decision matrix for deployment.
Options are also detailed in the OCS AD Guide: Active Directory Global Settings and Objects.