Confusing Terminology in Calendar View
This has cropped up a number of times from customers.
They are confused. If you look at the Calendar View, there is a widget on the left called "Activity Types" which contains things like Events, Todos, Opportunities etc...
When you are Editing an Event, there is a field called "Activity Type". Customers expect that the Calendar will display the various Activity Types of the picklist in the Calendar View Activity Type view so that Calls, Meeting, Email etc would be rendered in a different colour.
The confusion is because both things are called Activity Type...