I have spoken at several conferences and written occasionally about opportunities for social games on (Web) networks other than Facebook. When I first moved into social gaming, some of the most exciting international economies (Germany, Brazil, Russia, Japan and China) were dominated by social networks not named Facebook. As the landscape has evolved, however, this opportunity is now less important for social game companies.
Outside of Asia (where I do not have nearly as deep a market knowledge as I do in other territories), once promising social networks are no longer worth the effort. The VZnet social networks in Germany lost millions of users and Facebook is now the best monetization opportunity there. In Brazil, Orkut continues to lose market share at a rapid pace to Facebook and I do not know of one non-local company who is making significant revenue on that platform. In Russia, Facebook is yet to gain a strong hold but US and European developers have very rarely seen significant revenue (you would be very lucky to generate over $1,000/day from all three Russian SNs combined). Hyves still monetizes well, but given the small absolute size of the Netherlands total revenue opportunities are limited. Other social networks (Nasza Klasa in Poland, Tuenti in Spain, Netlog, etc.) also fail to generate enough revenue for non-local developers to warrant the effort. And let’s not even bring up Google+.
As a reformed entrepreneur, I still find it difficult to leave money on the table. For those who want to release on networks outside of Facebook and mobile, I strongly recommend using a distributor who will do the bulk of the engineering and marketing, allowing you to focus on your core product. Otherwise, do not get distracted by these other networks and create the best Facebook or social mobile games you can.