"Wave was released in "limited preview:" too few real users not soon enough. Google+ is in "field testing" right now. The language here is important. "Field test" implies that a significant number of real users outside of the plex's walls are putting Google+ through its paces, and will find confusing UI around sensitive items like privacy before the product gets released to the public."

Using the right buzzword doesn't mean anything. And 'field testing' doesn't imply more users than 'limited preview'. In fact, I would have said it meant less, by my gut feeling. It probably doesn't have any relation at all in their minds.

For the rest of it, I think I can summarize with:

Keep it simple, while still implementing all the features necessary for social networks, especially Notifications and mobile access.

The only non-obvious thing is the feedback mechanism, which is apparently pretty rich.

I still say that it doesn't matter how nice a social network is if my friends aren't also on it. And if you let me in but make me wait too long for my friends, you'll lose us all 1 at a time, which is the same result as never having us in the first place.