First up we found this excellent post by Justin Briggs on seomoz.org that discusses the way that Google+ affects the Social Graph that Google is building.
Google Plus is Google's latest attempt at building an explicit social graph that they control, but Google has been building out an implicit social graph for quite some time. This graph is still relatively naive compared to the maturity of the link graph, but search engines continue to develop this graph. Since it is already directly influencing rankings, and its value will increase, it’s important to understand how this type of social graph is being built.
Justin then links to another great post by Bill Slawski on seobythesea.com that nicely complements the Social Graph article by talking about the issue of Trust.
When you interact on a social network, or write a review online or update information to an internet mapping service, how much does the service you are using trust the content that you add, or the changes that you might make?
All in all, these articles serve to reinforce the FACT that you need to be on Google+ right now if you have any interest in building a respectable online presence. Facebook and Twitter alone are not going to cut it in the (very) near future, especially when Google holds so many of the cards.