There are a lot of moving parts to the system depending on the components you have installed. How do you know if your system is healthy? Here are a few items to watch:
The Synchronization Service Operation tool should have no errors
MIM portal requests should show successful completion (Completed)
MIM SQL jobs should be successful
The Windows Application and Forefront Identity Manager event logs should be shown
SQL and/or clustering logs should be shown
The duration of synchronizations and imports and exports over time for each Management Agent should be monitored