Dive Summary:

• Between July 2011 and July 2012, Pinterest use in North America as increased by 5,124%, whereas Instagram activity has grown by 17,319%.
• In the U.K., Instagram activity grew 2,028% compared to Pinterest's 1,489%.
• Overall, Instagram skyrocketed above Pinterest's market share growth, affecting additional areas including Singapore, New Zealand, and Australia. 

From the article:

Pinterest and Instagram have taken over in the race among niche social networks, both experiencing astronomical growth rates around the world.
While Facebook and Twitter should be expected to continue their reign as leaders in social, these alternative networks are growing in popularity, according to a new data. ...