Exchange Domain Servers and Exchange Enterprise Servers groups
If you have installed Exchange 2000 or 2003, then you have probably noticed that the SETUP /DOMAINPREP process creates two groups in the CN=Users container in each domain. These groups are the domain local group Exchange Enterprise Servers and the global group Exchange Domain Servers.
Do not delete these groups and do not move them out of the CN=Users container.
I have dispensed this advice over and over again, but still I come across problems caused by an over-zealous administrator. Moving these groups will produce errors and will cause the System Attendant to either fail or not restart. The solution is to simply move the groups back in to the Users container. See KB article 260914 "Domainprep utility does not work if Exchange Enterprise Servers group and Exchange Domain Servers group moved to a new container" for more information.
I just saw this again today, so this seemed like timely advice.