I agree that the "whole calendar" notification is probably overkill.
But if we are building this thing, might as well make it as flexible as possible.
For a simply piCal installation, the "whole calendar" is an easy way for a user to get reminded.
For a fairly complex piCal install with loads of categories, still thing a "for this category" would be useful.
My first use for this feature will be a School District site -
Union City. Having the ability to do categories, or in this instance an entire school, would be useful to parents.
I'll keep you posted on our progress.