To enter the contest, participants visit the #GetGrounded board on Vibram's Pinterest page and comment on any photo that motivates them to lead an active lifestyle. They must then re-pin the photo to one of their own boards and include the #GetGrounded hashtag, which has been proliferating across the web on other social platforms such as Twitter and Facebook.
The contest is just one element of a larger campaign initiative to encourage their community to get outside and stay active. Vibram has also created an inspirational video piece to augment the contest, as seen below.
I think Pinterest is the perfect platform to host this contest due to its functionality and visual nature. Whereas Facebook requires the user to click through a photo album and view user photos and comments separately, the Pinterest interface allows the user to see many photos and their accompanying comments all at once, as shown below. By requiring that the contestant re-pin the photo to their own page, Vibram is also helping to extend the contest to a larger community.