The evidence that Google+ wasn't ready to be a Facebook killer is that it is invitation only. Living in a college town, I was around Facebook when it was exclusively for students. Facebook's growth from exclusive to pervasive was enabled by the fact that students move on get married and have babies - looking at pictures of her first granddaughter is what sold Facebook to mom.
On the other hand, the bloggers and programmers invited to Google+ will remain bloggers and programmers. They're already married and have kids and more importantly already update Facebook with photos for grandma and uncles.
Don't get me wrong, Google will make money off this thing even with limited adoption and the assumption that it will ever roll out of perpetual beta (or preview in this case) is not a settled matter based on Google's history.