We recently replaced our Windows Server 2003 Active Directory with a Windows Server 2008 one.
The problem we're facing is that suddenly each network seems isolated (in the Microsoft Windows Network domain) and workstations/servers can only see their own network (for example 192.168.2.* can only see PCs on the 192.168.2.* and so on).
This doesn't affect the overall network since most of the services between servers and workstations work fine but certain software rely on the Windows Network to discover PCs (most importantly McAfee ePolicy orchestrator).
I'm not pointing the Windows Server 2008 AD as the source of the problem but it immediately occurred after switching to the new AD.