Date: March 10, 2012 07:31PM
"I actually emailed pinterest about this because I wanted to be able to have private boards for business purposes and to also block certain people for gifting purposes. I received a personal reply pretty quickly saying they get requests like that often, but at this time there aren't really any privacy settings. I think it will come eventually but since pinterest is so new, they just aren't there yet and the point is to share. I've thought about creating a seperate account using my business email address that maybe I could use for those things."http://community.babycenter.com/post/a29160961/ot-_can_i_block_her_on_pinterest
So I think you're SOL -- sorry.