I realize I’ve been posting about Zynga’s Farmville a great deal, but the speed to which it has grown to be the number one application on Facebook really is an impressive story. Yesterday, Farmville was the first application to break the 7 million level (hitting 7,259,378 daily active users according to Developer Analytics tracking) while no other application has yet to cross 6 million.

Slashkey’s Farm Town maintains it’s hold as the #2 application and continues to grow, but at a more gradual pace. Farmville’s most recent push can be tied to the release last Friday (August 7th) of achievements (presented as ribbons) that help define progress in the game. Users can earn ribbons for raising multiple animals, crops and trees as well as several other tasks.

It is fairly common for game applications on Facebook to prompt users to “brag” about these achievements, which in turn gets users to promote the game to their friends. But the ingenious twist that Zynga developed was providing an incentive to post the achievement to your news feed and for your friends to click on it.

Instead of the “brag to your friends about your achievement” pitch to get users to post to their walls, this is all about “sharing the wealth” with your friends. And on the friend side, they see that the poster “wants to share their success with you” and there is a distinct “Get a bonus from Eric” link that prompts users to click and get back into the game.

The phrasing is subtle, but it actually transforms what some call spam into a message that provides value to both the poster and the friend. As a result, in just two months, Zynga’s Farmville has grown to be 34% larger than the number 2 application, Farm Town. Expect other games and applications to take note, because as marketers and applications fight to get users to post into an already crowded friend news stream, it’s the ones that deliver value that will cut through the clutter.