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Here is a good post that tells you how to optimize content for social sharing: http://www.seomoz.org/blog/rock-your-seo-with-structured-social-sharing-mozcon-presentation

The post says: 150x150 square is the best size for both Facebook and Google+. The height must be at least 120px. (If the width is less than 100px, then the aspect ratio must be no greater than 3:1.)

-Joey

Awesome tool. How can I tell which links to my site I should disavow? We get a bunch of random links per day that look spammy, but how can I tell for sure that removing them will help rather than hurt?

It's definitely possible to get Google authorship for a PDF: https://plus.google.com/+MarkTraphagen/posts/j7rN1AWzAK5

But I can't figure out how to do it! Anyone know?