calendar still has no internal tooltip implemented. and as far as I rememeber it's even removed from interface. use rich:tooltip.
I am too using the organizer example from the demo site. Am having some problems to access the implementation of the CalendarDataModel interface. I am using seam. How have you accessed the implementation from the dataModel attribute of the rich:calendar tag
Tried rich:tooltip also, with no success. I guess it is just not possible.