PFC, also known as PlayFish Cash, lets players buy items in the Build menu that have a green background.
PFC can be bought though Paypal or a variety of other retail sites.
The average user spends $60 (USD) per year on virtual goods. Users who spend $1,000 (USD) in a year are known as "whales" and are much desired by software developers.
There is a rare category of Super Whales that spend more than $10,000 (USD) per year. As of June 2010, there were only five "super whales" on the entire planet.