This produces a database approaching a petabyte in size. How much is a petabyte? One petabyte is equal to 13.3 years of Hi Def video or 20 million 4 drawer file cabinets filled with single spaced pieces of paper. One petabyte = 1000 terabytes. Basically, more than you can imagine.
Some background on Zynga, the creator of Farmville, Mafia Wars and a few other very successful facebook games. Zynga hosts 250 million active visitors a month to it's games. How in the world does Zynga make money you ask? Well, let's take Farmville for example. There are about 31 million players a day on Farmville. Zynga sells in game coins - these coins allow players to differentiate their farms from the masses with special items, flamingo-shaped topiaries are especially popular. These coins are sold either direcly online through the game (just give me your visa card or Paypal account), or via game cards (available all over including even grocery stores). 7-11 even had a promotion for awhile on their slurpee cups. Redeem the sticker on the cup for special items. You can imagine how much revenue Zynga made just from the royalties on the cup!
I know - you're asking yourself, seriously, do people really pay for in game virtual items? Yes, they do. This has been going on for years now. I remember paying about $20 on ebay for a set of very cool virtual armor for a good friends birthday for her to use in the online role playing game, Asheron's Call. Back to Farmville - let's say that Zynga manages to get a penny a day from those 31 million people. 3.65 x 31 million people = $113 million a year. That's a lot of revenue. Multiply that by the number of games they have and they are making some cash.
These games are using some very state of the art technology for managing all that data. Farmville uses a new data management system based on open source called CouchOne. Stupid name..... So yes, Zynga and other game makers have overhead. Servers, datacenter costs, maintenance, large Internet pipe charges, and a team of designers to keep their cash cows (pun intended) interested in the game by constantly updating the game with new challenges, items, and what have you.