It's no secret that the primary source of income for social games is in-app purchases. As a model, it works just fine. Sometimes, though, other models work better for certain games - like the subscription model, for example. It's coming to Facebook soon, and developer KIXEYE's game Backyard Monsters will be one of the first titles to feature it.
There's a whole segment of casual gamers out there who have gone unserviced until now. GameHouse has announced that they are opening up their unlimited play FunPass service to Mac users, which currently brings all-you-can-play access of over 1700 titles to PC gamers. The service is free to try for seven days, after which time you can pony up $19.99 for a monthly subscription.