Antonio,
The Revenue piece is completely unrelated to the Employee's Org. Unit. It is actually determined based on the Sales Order that serves as a basis for Invoicing.
As for Costs, there are two components:
1) The debit portion will be sent to the Cost Center that is Responsible for the Project.
2) The credit potion is used to offset the Employee's Cost Center.
The logic behind this is that when you post Payroll expenses, you'd post them to the Employee's Cost Center. The intention is that by an Employee posting time to a Customer Project, it will automatically post the debit of the expense to the Responsible Cost Center (to track which cost center truly incurs the costs) and also offsets the Payroll expenses via the credit to "Service Expense - Internal" account. So by combining the Payroll Account and Service Expense - Internal offset, it automatically gives you what portion of the Employee's cost truly belongs to their home Cost Center (and what portion was incurred on behalf of other Cost Centers)
Note that for Customer Projects, this is dependent on Revenue Recognition occurring. For Internal (Cost Collector Projects), these postings happen immediately.