Zinga have done a phenomenal job with their games and the art of tempting consumers to pay real money for virtual goods. On my inital reasearch of Yoville I found that many players were spending at least a $100 a month on virtual goods through this game alone I found some that claim to spend $1000 a month on a regular basis right upto $5000 dollars a month for one player. With over 5 million active monthly users for Yoville alone (the last time I heard) they are pulling in some nice revenues.
The way they have generated revenues through brand marketing in this game is by offering players free yocash (which players pay for at a rate of over $10 for 50 yocash) when they sign up with brand x, the majority of which also need the player to purchase their services or put a cc on file. They ended up in a lawsuit at one point as a members credit card was billed for over $200 for offers she completed to receive YoVille currency.
However they could take this much further with a much more effective strategy than they are doing now.
