If you plan to move the GC role from a exchange 2010 servers to another Active Directory member server in the domain, be aware that there is some registery tweaks you should know of.
If Global Catalog was enabled on the Exchange 2010 server, the port for Exchange Adress book have been set static in registery. When you remove the Global Catalog role and restarts the server, MS Eschange Adress book service will not start and therfore mail clients without Cached exchange mode have problems connecting to the Mailbox server.
You will see the error:
Unable to register the MSExchangeAB RPC interface. Failed with the error code The endpoint is a duplicate (1740)
To fix this locate this Registery:
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\NTDS\Parameters\NSPI interface protocol sequences] and search for a port bind eg. 6004.
DO NOT toutch this if the server is global catalog, if it have been global catalog in the past, you can delete the key and restart the server.