Bloomberg Intelligence estimates Facebook has done well with its 2012 billion-dollar purchase of Instagram. If the photo-sharing service were its own company, Bloomberg Intelligence analyst Jitendra Waral estimates Instagram would be worth $100 billion, a 100X return on its $1 billion purchase. Earlier this week, Instagram surpassed 100 million users and is on pace to double that in five years. The reason for the bullish estimate: The youth-skewing photo site is still growing in the United States, unlike its parent company. That’s appealing to advertisers.