Are there any examples or case studies of social games, specifically on Facebook, where the developer has made drastic changes to the economy? I'm specifically interested in examples where the old economy was based off of purchasing items with Facebook credits then moving to a new model where the same inventory or similar inventory is sold with a soft currency. The closest comparisons I've been able to find so far are looking at iOS games that have gone from purchase models to freemium models, but haven't found a comparable scenario in a social game besides larger scale MMO's.
There is a great presentation by Ben Cousins called Playing To Win. On slideshare (with narration) - http://www.slideshare.net/bcousins/paying-to-win
It describes the case of Battlefield Heroes game which was very popular but didn't monetize well and how they redesigned the entire virtual economy ecosystem to make it better. The main changes they did were:
This is not a facebook game but the same principals apply. In order to optimize and balance your virtual economy ecosystem you need to have at least two currencies and flexible ownership model.