Can a task be assigned to user?
Yes, you can assign an activity to any number of your account users. You can even create tasks from email messages, and delegate them to the people you work with — without forwarding email!

Yes, you can assign an activity to any number of your account users. You can even create tasks from email messages, and delegate them to the people you work with — without forwarding email!
You can, but you don't have to.
Not currently. We may add this functionality in the future.
A department calendar shows tasks for all contacts in the department. Contact calendar displays only tasks associated with a given contact.