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Rand Fishkin recently blogged on the effects of Google + and ranking performance. Video included... recommended.
It used to worth doing all this for Facebook traffic. This days when a user likes your site only a small fraction of the user's friends see the like in their feed. I know this because the number of likes my site pages get has been increasing over they years while the referral traffic I get from Facebook seems to be caped to a certain amount.
If I correctly understand what Rand Fishkin is saying, then apparently anyone with a lot of G+ followers could post a piece of worthless garbage, and it would soon start showing up at the top of those followers' search results.