Facebook is buying Instagram for a whopping $1 billion, said Instagram’s founder and CEO Kevin Systrom earlier today.

Instagram is a photo sharing service and app that we have been reporting on over the last few months. It is been wildly popular. Launched only about six months ago for Apple devices, it already has over 1 million users. The app was named Apple’s “App of the Year.” for 2011.

InstagramThe Android version of the app was released on Google Play just a week ago. According to Google, it experienced over a million downloads its very first day. The Android version has been rated 4.6 stars out of 5, by over 20,000 users so far.

But with Facebook buying out the company, what are users to expect?

Facebook is likely to tread gently after making that kind of investment in the service. Unlike other Facebook acquisitions, it’s expected that Facebook will keep the service running pretty much as is for the time being. Facebook says they will keep Instagram as an independent app.

Facebook Chief Executive Mark Zuckerberg wrote on his blog today that “This is an important milestone for Facebook because it’s the first time we’ve ever acquired a product and company with so many users.” He went on to say “We plan on keeping features like the ability to post to other social networks, the ability to not share your Instagrams on Facebook if you want, and the ability to have followers and follow people separately from your friends on Facebook.”

So short term, no major changes. But over time, watch for Facebook to integrate some of it’s own services and offerings into the app. For as with any investment, they will be looking for ways to make money with it.

What do you think Facebook with do with Instagram long term? Leave your comments below.