Inside Social Games has an interview with Facebook CEO Mark Zuckerberg. There are a couple of things there that discuss their games strategy. A few sample quotes specific to games are below, but the whole thing is worth reading.
On viral versus retention (“viral strength… optimizes for apps that are very viral instead of apps that are high quality and that people want to reengage”):
…we intentionally weakened the viral channels recently, and intentionally strengthened reengagement with emails, so that there will be better apps.
On small companies succeeding: