Sgt_Kickaxe - 4:55 am on Jun 2, 2013 (gmt 0)
I gave it a shot and saw no initial rankings gains for my niche. I didn't really expect any since the number of people who enjoy that niche on Google+ is nearly non-existent.
After roughly 3 weeks I noticed that any new article I wrote that contained images was being scraped and that I was being outranked by new sources for these. I shut down the account after two months, removed all of the G+ buttons and links and my entire site started receiving about 10% more traffic starting 10 days later, especially on new articles.
While that isn't scientific an observation and other factors could have come into play I can say for certain that I got no boost from G+ and that I gained a little traffic when I removed it all, including authorship links. I told myself that I would not give it another shot for at least a year and then only if others began raving about the effects first.
I'm fairly sure Google doesn't want G+ to become a rank influence, or at least they don't want to attract the sort who would use it as one.