This is the disclosure that comes up when you register for the promo:

"Marriott Rewards Plus Points will receive the following info: your public profile, friend list, email address, News Feed, relationships, relationship interests, birthday, notes, status updates, checkins, education history, events, groups, hometown, interests, current city, photos, questions, religious and political views, personal description and likes."

Also its only select Marriott, Rennaisance and Autograph properties. No Ritz-Carlton or other Marriott-owned.
I like free points, but I think I will pass.