Add-on commenting systems like Facebook Comments enhance the user experience, but can make it harder for search engines to index content. Most third party commenting systems leverage javascript to display information and add bells and whistles. However, Labnol.org reported that now Facebook Comments are being crawled (and ranking) in Google’s SERPs effectively breaking the mold for third party commenting systems and rankings:
Facebook Comments can be displayed in a few different formats, XFBML (Xtended FaceBook Markup Language) and HTML5. While the report references that Google is crawling comments embedded in an iframe, that specific functionality is not supported for Facebook comments. 
We performed some tests and can confirm that many of the comments are in fact showing up for articles. Here’s a search for a comment on the Raven blog that uses an XFBML implementation of Facebook Comments:
So look for Facebook Comments showing up in Google results. If you would like to give your comments the best chance to rank, go with the XFBML implementation as that type is what has been shown to rank.
We performed some tests and can confirm that many of the comments are in fact showing up for articles. Here’s a search for a comment on the Raven blog that uses an XFBML implementation of Facebook Comments:So look for Facebook Comments showing up in Google results. If you would like to give your comments the best chance to rank, go with the XFBML implementation as that type is what has been shown to rank.Postscript by Barry Schwartz: Matt Cutts of Google confirmed this behavior and added Google Can Now Execute AJAX & JavaScript For Indexing.
Related Topics: Google: Social Search
Greg, thx for the article, it’s a nice way to use XFBML on SMO to help with SEO ;)
This can be a rush of visitors to site owners, for when they comment with a link back to their niche market.
what if you don’t want your comments to be searchable? hoping Facebook adds an opt-out feature here.
XFBML and FBML are being eliminated in the next few months, you’re better off going with HTML5 longterm.
Great for SEO, but what about the reputation of your brand / company? I mean, if the comments are indexed by Google, bad comments may also appear first in the search engine.
It would be interesting to know whether it is possible to choose the comments you want to reference.
On the other hand, this may influence the perception your customers have of your company On the other hand, this may influence the perception that your customers have of your company and compromise your transparancy and your credibility.
Should think about it!