Comparing Facebook Like vs. Google +1
Like vs. Google +1: What Are The Main Differences?
As Google product manager Daniel Dulitz mentioned, Google +1 is an annotation system which reinforces the interactions between organic and paid results, web pages, and your Google contacts.
That being said, your Google contacts are not necessarily your friends… and, you need to have a Google account to fully utilize the +1 feature. As a result, Google +1 acts as a collective rating system helping results be more trustworthy, but not adding the social infrastructure.