Allow users to categorize content, and publish their categories

Hi,

Been playing with drupal for a month or so. Now i'm stuck on one of the main features of the (future) site. I would like to

1. let users create their own categories and collect nodes to one or more of these categories
2. let the user mark categories directly from the node page (not the node edit page)
3. have the category lists private by default
4. let the user make a category list public to either all auth users or to particular groups of users

I've struggled with private taxonomy and community tags but I can't quite get what I want. I've also failed with flags, but maybe I should give it another go?

I'm sure this can be done with a combination of all the excellent modules out there. Maybe someone can point me in the right direction?

Thanks!
/asa