A new month, a new milestone for Instagram. Mashable is reporting that according to the photo sharing app's API, it has now surpassed the 50 million user mark and is adding new users at a rate of around five million a week. The news comes not long after Instagram hit 40 million users, which of course followed a big few weeks for the company. First it launched its much anticipated Android app — which was downloaded more than a million times in less than a day — and then Instagram became a part of Facebook thanks to a $1 billion acquisition deal. Even the iOS version of the app saw a surge in popularity, reaching the top of the App Store charts last month for the first time ever. Now the question is whether or not it can keep up this momentum — and how long it'll take before we see Instagram reach 100 million users.