Google indexes Facebook pages based on your privacy settings; if some things are set as public, it may be crawled. The best way to find out is to get the URL of your Facebook profile and then go to Google and search for it adding the prefix "cache:" in front of the "http://www.facebook.com..." etc. Then you can see exactly what Google is crawling from your profile.
Even if content is hidden on you own Facebook profile, if someone "liked" your post and shared it in public parts of FB, it would then be indexed.
However, the relationship between social networks and Google keeps changing. In the past, Google has indexed all Tweets, then Twitter changed the relationship. Google will crawl any parts of a site that the site lets it crawl (and will sometimes sneak in the back door). At the moment, Facebook is something of a walled garden, shutting itself off from the rest of the web, but as it seeks to justify stock prices to its stockholders ;) it may be under pressure to monetize in new ways. That could mean taking down some of the walls and letting search engines crawl every post and send more traffic to it. (It has changed privacy settings about what's visible to the public and search engines many times, usually on the side of showing more than what was visible before).
And on the third hand, I think people are running scared about the duplicate content issue a little too much. Syndicated content gets quoted and requoted around the web. Google's algorithm may be smart enough to comprehend an excerpt with a link back to the original article -- X is someone pointing to Y article.
I'd come at the question sideways and ask: what is appropriate and typical on Facebook? Would your friends or Facebook members enjoy reading a few featured highlights? Or would they find it annoying to have their wall spammed with excerpts of your articles planted for the purpose of attracting traffic? What would your followers find interesting, and what would be intrusive?