While the developer of Facebook for the iPhone & iPod touch famously quit in 2009 because he disliked the App store and its policies, the app has lived on. Recently that app has 100 million active users and shows no sign of slowing down.

While Facebook has remained one of the top free app downloads since its release, it is one of the lesser-updated apps. It has no iPad or universal version and generally lags behind when an iOS update comes out. Despite this, the popularity of Facebook itself have driven this app’s popularity. What’s really impressive about this number is that Apple announced it had sold 100 million iOS devices only a few months ago in June. That means virtually every person with an iPhone or iPod touch is running the Facebook app. It is even reported on 9to5mac.com that of the time iPhone users spend on third-party apps, more than half of it is on the Facebook app.

The timing of this milestone comes on the heels of a recent app update to support iPhone 4 and iOS 4 features, as well as the controversial “Places” feature. With Facebook Places, you can “check in” to locations much like Foursquare or Gowalla, but in Facebook’s version you can actually check other people in to locations by tagging them. Some people do not want their location shared online, and it is enabled by default. Luckily, like every other new controversial feature they’ve added, this one can be turned off easily.

Based on Facebook’s numbers, virtually every one of our readers uses Facebook. So let us know in the comments if you think Facebook is an essential app and what you want to see in future versions. If you do use Facebook, make sure you’re a fan of AppAdvice to get all of the latest news and updates on your Facebook page.