My calendar contains appointments. Period. Nothing else.
(Appointments includes birthdays, anniversaries, vacation days and holidays.)
Recurring tasks for which the exact day doesn't matter go into Sciral Consistency.
Deferred tasks go in my tickler file or on my NA list with a future date, as appropriate.
Deadlines go into the information file for the appropriate project, or into the tickler file, as appropriate. ("Conference report due July 8" goes in project information, because the report requires lots of preparatory work. "Pay estimated tax June 15" goes in the tickler, because it requires nothing except writing the check.)
Katherine