According to Techcrunch, there are now 16,000 apps on Facebook, and its hard to get noticed unless your a high profile app developer, or associated with them. Some of these such as Slide are charging develoeprs $.50 an install.
But now we are beginning to see networks starting to form across specific application genres.
In the social gaming category alone, a battle is brewing between the Social Gaming Network (SGN) and Zynga. Tomorrow, both will launch separate developer platforms for other gaming applications. The appeal to smaller social game developers is similar: join one of the gaming networks and see your game promoted on the toolbar or gaming page when people are playing other games in the network. Fred Wilson, the partner at Union Square Ventures, who invested in Zynga, explains to me:
It is the exact same value proposition why you would want to build your app on Facebook as opposed to the Web. You can rapidly develop an audience. It is access to audience and monetization.