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There is already a big market open for business for +1's. I bought some for a site just to see what happens, can get pretty much unlimited amounts for pretty cheap.. Will be interesting to see if it help with serps.
The +1 lacks that motivation. They aren't sharing the site with anyone.
With all the years of experience, Google has, I think they have systems to give each +1 a value in the same way, they give each link a value.
I still have the Google + button my site... but does anyone really think this is ever going to take off?