[erans]

We've been analysing sharing patterns for a while. We tend to see that Twitter shares correlate too much with the amount of posts per day which may indicate its more bot driven.

FB Likes and +1 are much harder to fake and seems to correlate more with actual human traffic.

From our experience +1 tends to be factored into Google search results so there is direct value in having +1 on your site and having your visitors who like the content click on it (not to mention it gets circulated inside Google Plus itself).

We are working to add more sites as we go along and we would be happy to share some information about patterns across sites and topics.