> I'd really like to know everything FB tracks on those like buttons, it's probably an obscene amount of personal data.

When you request a page like this guardian article, all they'd have access to would be:

  * The url you requested, along with time and IP            
  * Any facebook.com/facebook.net cookies you have stored      
  * Any other headers your browser sends       
  * Metadata about the page itself that the publisher publishes via "og:" tags

Said og: tags look like this: <meta property="og:title" content="Facebook ordered to stop collecting user data by Belgian court"/>

How does that compare with what you meant by "obscene amount of personal data"?