It's always been one of the major problems in my applications:
Keep the model instance at multiple clients in sync so that people don't see stale states
The code required to make was huge, error prone and didn't solved all corner cases.
Switching our applications to CDO solved this problem because it is an integral part of CDO.
The other major problem CDO solved for me the problem of transfering only certain chunks of the big object graph and lazy loading other nested stuff once it is needed (one of the major problems in 3tier applications who are based upon models)