Google has now started to index not only your Facebook business pages but also Facebook Comments on your blog.
In a blog post by Amit Agarwal at Labnol, he explained that:
However, it looks like recent developments with Google algorithm shows that, “Googlebots, or the spiders that crawl web pages, are now reading Facebook comments on websites just like any other text content and the more interesting part is that you can also search the text of these comments using regular Google search.”
He even shared an example of how Robert Scoble’s comment on Techcrunch (which supports Facebook comments) was indexed and even found on normal Google search.
Now there is no reason not to use third-party commenting systems like Disqus, Facebook Comments or Livefyre because they actually help increase the interaction in your blog and especially now that they are even being indexed by Google.