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This is what Adsense's Team said:
A few months ago we released the +1 button on English search results on google.com. More recently, we’ve made the +1 button available to sites across the web, making it easy for the people who love your content to recommend it on Google search.
Today, +1’s will start appearing on Google search pages globally. We'll be starting off with sites like google.co.uk, google.de, google.jp and google.fr, then expanding quickly to most other Google search sites soon after.
We’ve partnered with a few more sites in Europe, Japan, India, Australia and New Zealand where you’ll see +1 buttons over the coming days.
You can add the +1 Button to your blogger blogs by reading this tutorial: