Google+ allows Google to further improve it's mission to organize content and make it accessible and useful, as it can rely on the people doing that work.
Facebook is all about connecting people. Google+ goes further. It connects people and content.
Let's have a quick look at those two giants. Zuckerberg developped Facebook to stay in touch with friends. Probably it was all about finding a date and staying in touch.
"Facebook's mission is to give people the power to share and make the world more open and connected."
Google on the other hand was founded by Page and Brin. They just wanted to improve search results provided by search engines.
"Google’s mission is to organize the world‘s information and make it universally accessible and useful."
What Google+ could do to search results
Google has a very waste ecosystem of applications: Gmail, Google Reader, Google Docs, Picasa, Maps, News and a bunch more plus their latest baby Google+. Google is all about organizing content and making it accessible. Looking at all those applications it could be scary to see how much Google knows about you. Using all that data allows Google to create a nice data profile.
Google+ will take Google a step further, by allowing Google to connect those data profiles. With Google+ the user actually orders the information. The user does Google's work, by sharing content, by commenting on content and by liking content. Obviously an article/website that is much liked and shared seems to be more relevant -> this will influence search results. Google could even analyze how content is being shared in circles to affect search results. Example: A circle called "friends". Most likely I have some common interests with the people of that circle. Let's use that information to display search results, by using content friend B and C has liked.
The next Google search interface might be looking like this
SEO will be hard to control
A couple years ago SEO it was all about keywords. Keyword density and the kinds of keyword you chose. This will soon be over. Search results will be highly customized. There won't be a single user having the same results as they are all based on their social profile and their activities in Google+ and friends activities. It will all be about "how much has the article been shared".
So, these were just some inputs. I'm not a fortune teller, but these are things how they could become. We will see very soon.