But taking a random sample of people and getting a hopefully-large-enough subset of their friends is not what you want for a social product: you want all of your friends in it, or you just get frustrated and go back to your previous solutions. Facebook /nailed this/ with their multi-year long staged rollout by targeting colleges: already self-contained social ecosystems where almost all of a student's friends are going to be other students; you start with one college, then two, then slowly ramp up until you can flip the big switch. Google simply does not understand this, and keeps falling back to their experience with Gmail, which was a fundamentally different beast.