Well, of course some people noticed that Instagram hit 200 million users, but Facebook made the announcement the same day they said they acquired Oculus VR, and that, understandably, is the more surprising news.
If anything, reaching the milestone was inevitable: Mark Zuckerberg obviously knows what he's doing, and by letting Instagram run itself independent of Facebook, it has remained popular, even more so than it was before. The company added 50 million users in the last six months alone, which is an awesome feat. Zuck even dropped the news during a conference call to answer questions about the Oculus buy, instead of setting up a separate conference call (or letting Instagram's CEO do it.) Facebook also announced that over 20 billion photos have been uploaded to Instagram—it's a runaway freight train that they're happy to let loose.