We’ve been expecting LivingSocial to become the top application for a week or two now but as of today the statistic is official. With 20,009,207 monthly active users, the application has surpassed Causes who has dropped to 19,930,177 monthly active users. We haven’t been able to put our finger on the reason of the massive drop by the leading application but whatever the cause, LivingSocial has leaped to the top of the leaderboard in just a couple of weeks.

There’s no doubt that you’ve seen the company’s popular “Pick 5″ application and more recently they’ve launched “Picktacular” which is a crowd-sourced version of the old game Family Feud. Prior to the redesign LivingSocial has a suite of applications that were relatively popular but the company has experienced unheard of growth in just a few weeks.

The growth inspired other companies to duplicate much of the functionality provided by the “Pick 5″ application. It’s more than reasonable for large applications to duplicate the successful features of other top applications but to companies in particular literally duplicated the Pick 5 functionality feature for feature.

It’s still too early to determine how things will pan out for the Facebook platform and how many of the previously leading applications will fare. What has become clear is that all applications must develop creative ways to incentivize users to publish feed stories as those stories have become the primary driver of new installs. If your application chooses not to publish feed stories, you can kiss your chances of huge success goodbye.

It will be interesting to see how large LivingSocial can get as the application continues to add close to a million users a day.