In Sync indicates that there have been no changes to local public folder replicas
since changes were last sent.
Local Modified indicates that there have been changes made to local public folder replicas that have not yet been sent. So if you see the local modified for Exchange 2003 server there is no need to worry, if it is for 2000 it means that there are changes yet to be replicated.
As far as best way to know if replication completed, I rely on looking at the size and number of items in the local public folder store for each PF and compare both source and target store (This is not feasible in large environments and you might need to export the list and compare using excel).
thanks,
