With more than 250 million users, there’s no doubt that Facebook is truly a powerhouse to be reckoned with. With this massive amount of users flowing through the site, cornering the lucrative casual gaming market would be a triumph. While I’m not sure we’re ready to proclaim a flag raising winner, Zynga is clearly leading the charge, and recently announced that they’ve surpassed the 100 million user mark. Doing a quick look at the numbers, that means that almost half of all Facebook members are, or have at one point, used a Zynga built application.

Released on June 19th, Zynga’s current runaway hit FarmVille is primarily responsible for this boost in usership. Just last month, Zynga proclaimed that FarmVille was the “largest and fastest growing social game.” Two points to Zynga for being dead on with this statement. In a new chart published by Inside Social Games, Zynga claimed 4 out of the 10 top spots in most active games on Facebook.

With over 12 million active daily users, or roughly 5 percent of the entire Facebook population, FarmVille has almost doubled the previous ‘farming’ based app record help by Slashkey’s Farm Town. To this end, one thing is becoming increasingly clear: Farming is big business. As with iPhone apps, previously the hot spot to be was the ‘Mafia’ wars type games. We’ve seen a number of derivations (or, less politely; copies) of this form of play, right through to market saturation. Whether it was consumer complacency, or this market saturation, over the past few months, there’s been a shift away from bullets and bombs to water and seeds.

We could now be on the verge of another ‘derivation’-fest, as Zynga borrowed more than just the name from Slashkey, and likewise, casual games maker Playfish has launched their own farming app titled Country Story. In just under two weeks, Country Story has gone from 1.4 million active monthly users to 4 million. With 9 farming based titles now in the Facebook application store (within the top 109), in total there are 72 million active monthly users on Facebook, or approximately 29 percent.

Zynga is already the current app developer for Facebook, and these new numbers are just another award on the shelf for the firm. If measured by the typical benchmarks used for startups: audience, page views, growth, etc., it’s a fair statement to make that Zynga is an overwhelming success. What’s even more impressive is that the casual/social games maker is managing to do inside Facebook what the company has yet to do itself: be profitable. Remember, Zynga leverages the power of microtransactions to generate revenue, while at the same time allowing users to purchase any number of character customizations. Estimates place Zynga’s annual revenue around $100 million for this year alone, while Facebook’s estimated value is around $500 million. However, as stated above, Facebook isn’t making any money. So when viewed through these glasses, who’s really getting the better deal here?