Generating private content

Hi drupaliers

I'm wondering if there's anybody that can give me a pointer about how to go about providing certain functionality to users of a drupal site. There's other aspects to the site but the one I'm struggling with is this:

- there is a list of around 100 statements which each belong to one of 10 or so categories
- each user can give one of three possible answers and can add comments to explain their answer
- the user needs to be able to add new statements to any category which are unique to them
- the user needs to be able to go back at a later date and update their answers
- the user needs to be able to view all the statements they have answered in the same way
- each users answers need to be viewable by only themselves

For me the crux of it is making each persons content only viewable by themselves as this goes against they way you'd normally want a site to work. I've thought of various ways of using taxonomy, profiles or surveys but none do everything that is required.

Any pointers appreciated....