There are some valuable content related to the Project Server 2010 Time-sheet and Task data flow been added on the TechNet site, including videos. I have witnessed frequent question posted on the Forums regarding Timesheet and Tasks management, also after the introduction of the great new feature of Project Server 2010 SEM (single entry mode). I believe these videos will be of huge help to the users to understand the concept and functionality of the timsheet and task management.
Also, i want to take the advantage and remind you about the work-flow diagrams related to the same topic posted a while ago on the TechNet forums, click here to access.
Below diagram, and more you can access from the above posted link, will certainly help you understand the data flow of the task and timesheet in a SEM.