Might be good for a quick dollar, but it's not sustainable.
Is there any information on how much money Facebook apps usually make? What are the earnings like on free apps that don’t charge subscriptions?
Applications with english users tend to be much better paid than other languages.
But it is easier to be visible in a less crowded market like Indonesia, or the recently growing asian countries.
I remember that on my ads (targetting french users) I was getting an eCPM oscilating between $0.06 on a RPG game and $0.40 on a quizz application which is quite low in comparison to the english application standards.
It also depends on the ad network you use (some ad network performs better than others depending on your application).
There is no generic rule. You have to experiment all of them to see which one works better.
I was making 15000 euros per month with 50K users per day on a RPG game (as opposed to casual game) using various monetization strategy.
On a quizz application, with 1 million active users per day (20 millions page views) I reached $3000 a day without any direct partnership (simply by adding a basic ad from RockYou) with ads only
