It may be hard to believe, but it’s already been two years since the Facebook Platform launched in May 2007. Since then, we’ve seen over 50,000 applications published (and tens of thousands more not published in the directory), significant changes to the way successful applications are designed, and a number of twists and turns – not to mention a lot of social and cultural change as people increasingly share more information with their friends.

Now, the Facebook Platform economy is estimated to be doing close to $500 million annually, and a robust ecosystem of developers, ad networks, and virtual currency monetization and payment services has developed to service the hundreds of millions of cumulative monthly active users on the Platform each month.

When the third annual f8 developers conference rolls around this year, developers will primarily be interested in learning how to build a sustainable business that leverages the distribution potential and social context of the Facebook Platform and Facebook Connect, instead of simply optimizing for short term virality. The next two years are going to be even more interesting than the first two!

Check out Facebook’s 2nd anniversary video: