Is It Possible To Store User Favoutite Category and Display Content Based on ?

OK, this is what I want to do:

Build a content rich site that also has directory style listing (real businesses). Each business will be categorized based on UK County name. Then users when registering will select a category (which county do you live in?) and then when logged in, below articles / sidebar it will list the businesses (posts) within that category.

I have searched for something and not found. I am guessing that it cannot be that hard to do, so may have to get something custom built via elance or something.

Are there any reasons why this may not work?

Are there any plugins that may do this, or very similar, already?

Many thanks

Jon.