Originally our network only had one domain controller. It is running server 2003. Last week I added a secondary domain controller to the network on a fresh install of server 2008.
The only thing that seems to be effected negatively on the network by the addition of the new DC is our exchange server that is running exchange 2003 on top of server 2003. One or two times a day, all of our employees that use imap to connect to the mail server are disconnected. When they try to recconnect is says that it can't resolve their username or password. This problem doesn't effect people who are using outlook. Restarting all the exchange and DNS services doesn't fix the problem. The only thing I can to to resolve the issue is to reboot the server.
Also, when this problem occurs, I can no longer remote into the mail server on a domain account. I have to remote in and log in as a local administrator or else it gives the message saying that it cannot log me on because the RPC server is unavailable.