For Utility: Facebook (and social media writ large) begins with the conversation as metaphor. Sharepoint begins (and ends) with the document as the metaphor. It was built with the belief that business users collaborate around producing documents. Social media presumes people have conversations. (I do apologize for picking on Sharepoint. Sort of.)
For Privacy: Facebook was designed for complete openness - its assumption is that we are in a brand new world, where everyone's information should be available to everyone. Google+ assumes people remain tribal, with shifting identities based on the circle of people with whom they are interacting at the moment. They spent 3 years doing sociological research, asking people to talk about the people with whom they have relationships. They heard people had an average of 4-6 "circles," each consisting of 10-12 people. (They obviously never talked to me.)
So Google+ begins with an assumption that you don't tell your mother or co-worker the same joke you tell your wife. You will have circles of relationships whose primary overlap is yourself. And people will move in and out of circles over time - a colleague becomes a friend, etc.
By starting with this basic principle - not trying to bolt privacy onto an open model (much like Sharepoint now attempts to bolt 'social' onto a document repository), Google not only answers the main criticism for Facebook, but it feels more natural as a result. (BTW, while it may not kill Twitter as quickly, it's aiming there as well.)
Of course, believing Google will respect your privacy is a bit of a gamble. Perhaps they are just a bit more clever about things than Facebook ever was...
Flickr image from 'shyb.' Happy Friday.