Picture-sharing service Instagram (driven only by the popularity of its free iOS app) has hit a whopping 2 million users already. As TechCrunch notes, the service hit its first million users in just three months, and six weeks after that, it has doubled that number. That's pretty astounding growth -- even other popular sharing services usually don't hit those milestones until a year or more after they start operation.
But Instagram certainly seems like it's hitting at the right place and time -- it's a super simple sharing service that offers a lot of features that tie in very well with all of its users walking around with connected HD cameras in their pockets. Instagram doesn't even have an Android app yet (though presumably we'll see one very soon), and also noted by TechCrunch, you can't even sign up for the service on the website -- it's all driven through Apple's iOS platform. That hints at quite a future for Instagram and its service.