Yet another User / Friend / Reader category request

My Suggestion
I would like to have subscriber list with multiple categories.
Posts and Pages and Links would be tagged with one or more categories and subscribers would only see the material that was in one of their categories.

Example
I want to create a blog for my school.

I have several categories of readers and would like to tag them as such.

“The Public” would see some informational posts.
“Students” would see those plus other posts, photos etc.
“Teachers” would see public posts, posts just for teachers, but not student posts.

You get the idea…
The more that could be tagged with this conditional system the better but I realize there will be a limit to what’s really feasible.