If they are data mining, they're not getting a lot from me - I only have a user name and a generic email entered, nothing else. You DO have the ability to have your account hidden from searches (i.e. if someone searches for "quilts", any that you have in your account will not be shown), and your email and personal info is never shown publicly.
It is similar to bookmarks on your computer, except Pinterest is visual, which is better for me.