Facebook announced today at Parisian tech conference LeWeb that Facebook.com was home to more than 350 applications with more than 1 million active monthly users each.

In a panel onstage, Facebooker Justin Osofsky also said Platform has been integrated with more than 200,000 iOS and Android mobile apps. When it comes to the big money-makers, Osofsky wrote this morning on the company blog, nine of the 10 top money-making iPhone apps are Facebook-integrated, and almost half of the top 400 iPhone and iPad apps use Facebook Platform.

Of course, there was a bit of light pandering to LeWeb’s heavily European crowd of entrepreneurs, developers, and technology enthusiasts. Osofsky mentioned to the audience that Paris is the number-two city in the world when it comes to Open Graph submissions for Timeline apps (don’t worry, San Francisco; you’re still number one). Also, he said that 40 percent of all submissions for Timeline apps come from developers in Europe.

A lot of Platform activity is the direct result of announcements Facebook made ages ago at its developer conference in 2011. At that time, Mark Zuckerberg told the audience about Facebook’s biggest-ever changes: all new Timeline-based profiles, functionality for listening to music with friends, wildly better graphic interfaces across the site, and something called Actions.

Actions represented an all new way for developers, brands, and publishers to interact with Facebook users, and by using Actions and integrating with Timeline, many app developers began to see huge bumps in user activity, from new signups to app engagement.

Given all that and the fact that the social network is now, at one billion users and still growing, the largst of its kind, it’s not too surprising that developers are putting Facebook first when building their apps — no more surprising than the fact that many developers are putting mobile first. They’re fishing where the fish are.

Top image courtesy of Jolie O’Dell