[jrockway]

I don't think Google necessarily needs to get all their users in one day of viral goodness like most tiny startups do. They have pleny of time and money to burn through; look at how long Microsoft has lasted. Google can gradually integrate their other products with Google+ so that you don't even know you're using +. One day you'll want to share something, and you'll already be on a social network, and it will Just Work. (This is especially relevant with smartphones. Think about further refinements of the Camera app's "instant upload".)

Anyway, I see slow growth for Google+. Most people don't want "social networking", they want to share photos with their kids or share funny jokes with their coworkers. Google+ will gradually integrate itself with services people use for this sort of thing, and will replace it as the "Tumblr feed" model replaces email, IM, and SMS.