AOL engineers are extensively using revision control in production environments.

Well. One thing for sure - subscription model won't work. It works only for AAA titles, others are gradually shifting to micropayments / microtransactions. (Yes, talk about buying an exp points and "money rules". It works, however, for both parties involved - players and devs/prods/publishmen).

As for sunk costs - terms can be discussed , venture capital can be found, even now, if they're having idea and half-assed implementation - they'll get funding to replace facebook ties (what are they, anyway ? authorization ? storage ? publishing ? ) with solutions of their own, then - marketing campaign and true profit in a year or two. They'll lose independence in the process, but that's the price.

Totally worth is. But forget Facebook and other closed platforms - go for your own infrastructure. Basically, what facebook gives developers is audience, an ability to quickly announce your project and make it known among huge auditory. This is a plus on early stages, but it becomes not so significant later, when you'll afford to advertise independantly and effectively, but Facebook-as-an-app-platform limitations will remain.
And one more thing - never, ever expect users to be grateful or pleased. I work for company developing and producing Web-based MMOs, and one thing I've learnt over years is - even if you'll hire hookers to give every male player in your project one head job - the only thing you'll listen from them is "why only once ?" - they are lazy, stupid and greedy.