On the news that Facebook will buy Instagram, smartphone users have flocked to online stores to check out what, exactly, was worth a cool billion dollars to the world’s largest social network.

On Tuesday, a message from the Instagram Twitter account said that the app had hit the #1 spot on Apple’s App Store for the first time ever. And in the week since it hit Google’s app marketplace, the Android version of Instagram has logged an impressive 5 million downloads.

That’s the same number of downloads as the company saw in its first six months, but not surprising given that more than 430,000 users had signed up to download the Android app before it was even released.

Looking at the numbers alone, you’d think that everyone was on board with the acquisition, but the Instagram fan base has been vocal about its opposition to the deal, saying that they’re worried Facebook will destroy the app that they’ve come to love. Others said that they have purposely avoided Facebook by using Instagram for sharing pictures with a select few.

“I don’t post photos to Facebook because of their ownership policy,” one user posted on Instagram. “Totally torn.”

As the New York Times’ Jenna Wortham noted, Instagram has been a place for folks to post photos that they don’t want to share as widely.

“I felt comfortable posting blurry shots from a pulsing dance floor at 3 in the morning,” Wortham wrote, “and no one ever faulted me for showing them what I ate for lunch — that was the entire point of the service.” Instagram doesn’t have a built in re-posting function either, meaning that your photos stayed with you and your account unless you chose to push them to another social network.

It will be interesting to see if other social networks built around smaller communities — Path, Diaspora, Hipstamatic— will see jumps in membership following this acquisition. For now, it seems like even if Instagram loses some of its current users, the visibility it gets from Facebook has already helped it a lot.

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