Submit/monitor tasks with Outlook

Hello everybody,
In an enterprise-wide deployment, which solution works better?

1- Submit tasks to resources via email?

2- (If possible) Send and include in Outlook calendar of each resource.

3- Primavera’s "Timesheets" module. How comfortable are users/resources with it? Can they merge their non-project activities (meetings...) in the same calendar (like in outlook)?




Thanks
Nozar