Start with: http://insertcredit.com/2011/09/22/who-killed-videogames-a-ghost-story/ It goes over exactly how farmville and similar games work, why they work and the entire theory and practice behind microtransactions. Everyone who is thinking of selling an app or a computer game needs to read it, if nothing else, just for the numbers.
Also, if you can tolerate it, here is his in depth review of Sims Social which extends the analysis (the web page design is actually extremely painful and hostile to readers, I'm not certain of the reason for the template he uses).
Next, with very clean numbers, again, is Congratulations, Your First Indie Game is a Flop
How much can your first indie game make?Lots more. His game flopped because of marketing failures, miss-steps, bad luck and, of course, it was a first game. But the numbers are interesting and useful.
This question has been answered many times in the last year and we now know some important things about full or part-time independent as well as hobbyist iOS game developers:
- The majority (median 25 percent) of their games earn from $1,000 to $10,000.
- If you're lucky, you'll be in the next 20 percent above that, earning from $10k to 100k.
- But you're more likely in the quarter below, earning only $100 to $1,000.
After that, well, I'll have to update ...