If you have three or more users whom you are going to set up replication relationships for, we highly recommend creating a dedicated synchronization workstation, so the system can operate without user interference.  If you make a dedicated synchronization workstation for this purpose, you should also consider marking a "synchronization service account" (like "zA2OSync") to maintain a higher level of security.  With a service account, one user does not need to have access to all the folders and mailboxes.