As told by tedbilly SharePoint is very sensitive to performance of DC specially when your farm and your DC are in different network zones.
If your farm configuration has this typology please be sure that your all required ports are opened on your firewall specially the Global Catalog port (3268 on TCP) wich allows you to perform searchs on your AD.





by: tedbillyPosted on 2009-02-24 at 00:13:08ID: 23719283
Sharepoint is very sensitive to the performance of Domain Controllers and yes it can take a LONG time to do this unless you configure profile import which preloads all the users into the Sharepoint databases and avoids the latency of querying the domain controllers.