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Two Google+ SEO guides by +Ian Lurie and +AJ Kohn you should definitely check out.
Hope Ocampo's profile photoDaniel Conrad's profile photoTim Buchalka's profile photoMyles Henderson's profile photo
If your audience isn't active, there is still a significant chance that your G+ profile and activity will effect the organic SERPs and have rich snippet data giving very good CTR too!
Agree with +Trevor Stolber . No matter what, search results will be affected by Google+ presence or lack of presence. Your business has to be on G+!
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