Are there are any studies that show what percent of users click the "share now" icons on a site vs sharing the content manually?  I personally never use those icons when I want to share a blog entry or funny pic or whatever -- I paste the link in to FB/Twitter/G+ and share it that way.

I'm curious if people use those often, if they're simply a good reminder to users that the content should be shared, of if they're largely useless.
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