Facebook Login is an easy way for developers to integrate an immediately recognizable login feature into their apps or Web site. The social network revamped how it handles Facebook Login back in April, and now more apps than ever are using the feature.

In a blog post released today, Facebook’s Jeffrey Spehar revealed that Facebook Login is now being used in 81 of the top 100 grossing iOS apps and 62 of the top 100 grossing Android apps. Even more amazingly, he also reveals that users log into new apps via Facebook Login more than 850 million times per month.

So, what does this all mean to the developer who has yet to integrate Facebook Login into their app? Well, it obviously means that you’re missing out. Spehar says that developers who follow Facebook’s best practices when it comes to Facebook Login can see their conversion rates rise above 80 percent. That’s definitely worth checking into if you’re a lowly app developer looking to get more people into your app.

To that end, Spehar shares two apps that are doing everything right in regards to Facebook Login. The two apps – Lyft and Kickstarter – are reaping the benefits of a simple Facebook Login process that only asks permission to access the bare minimum (public profile, email and friends list) while giving the user complete control over how often they want the app to post to their wall. Kickstarter even goes above and beyond what’s necessary by offering users the chance to try out their mobile app before choosing to share their Facebook information.

In short, successful apps that use Facebook Login must be courteous, transparent and reassuring. You’re asking to access a lot of information from your users, and you have to let those users know that you won’t abuse that access. With distrust of Internet companies at an all time high, you can’t afford to even give the slightest impression that you’ll abuse a user’s data.

If you want to learn how to properly integrate Facebook Login into your app, check out Facebook’s checklist and best practices.

[Image: Facebook Developers]