I just encountered Mike Melanson's ReadWriteWeb article Facebook Now Powers Comments All Around the Web (I love that in the opening sentence he refers to this as Facebook's "much-feared commenting solution"). The SEO in me immediately had to know, are these babies spiderable? Will Google be able to index Facebook comments as part of the textual content of the URL to which they are attached?
The Facebook Social Plugin page for Comments didn't address the subject directly, and was not particularly rich in technical details about how the commenting system works. Like others at that page (based on the example comments that were displayed there) I was unable to get the site code for comments to generate (amusingly, one user suggested a hack which put the code in an <iframe>). Doubtlessly Facebook will address the code generation issues soon; in the interim I decided to look in the wild for real life examples.
I began investigating by looking at one the early implementers of the commenting system, Sporting News, and found a recent article which contained Facebook-fueled comments. Viewing the source, only the call to Facebook was appearing in the code: the comments weren't (whitespace removed in the code snippet):
<div class="containerHeader"> <h2>Share Your Comment</h2> </div> <div class="facebook-comments" style="margin: 10px 0px 20px 0px;"> <fb:comments width="650" href="[URL]" numposts="10"></fb:comments></div> </div>
Since I don't see an <iframe> here I'm assuming this is an XFBML implementation, but as I'm not a developer there's every likelihood that further speculation will make me look like a fool. I enthusiastically invite my technically savvy readers to provide insight on how the Facebook commenting function works in my own (non-Facebook fueled) comments section.
One way or another it does not appear to me that search engine robots can index the text that appears in the comments section. Mi code es su code. Just to verify this, I looked at the Google cache of the aforementioned article, which fortunately contains a fully spiderable offset time stamp of when the piece was published and updated. Unless my calculations are off, if the comments were spiderable they would have appeared in Google's text cache, and they do not. I welcome any correction to my conclusion that Facebook comments are, at least in this implementation, not spiderable (and certainly if there is an <iframe> implemenation, those comments will not be indexed with the rest of the text for the URL on which the <iframe> appears).
If I'm correct there are clearly SEO implications for any site which may choose to use the Facebook commenting system. One of the endlessly-touted benefits of encouraging readers to comment is that these comments then become part of the spiderable content of a page, and as such are beneficial for search engine optimization: search engines observe that a page changes over time, giving them more reason to revisit it; short pieces become progressively longer as more comments are added; and, perhaps most importantly, the keyword universe of a page is both reinforced and enlarged as a result of the content that readers add (and these comments are as often as not likely to be semantically-related to keywords used in the post or article itself).
Additionally, it does not appear to me that there is any way that these comments can be referenced as permalinks. That is, many commenting systems (including the one used on SEO Skeptic) support permalinking of comments, usually as a hashtag anchor (e.g. [URL]/#comment-2554). This promotes the generation of links to particularly engaging pieces of content, as commenters or interested readers may link directly to a comment from an external source.
As a search marketer this would certainly make me hesitant to implement Facebook comments on most sites, particularly those which have a record of high reader engagement. But more generally as an Internet marketer, I can certainly understand the benefits of making comments personally meaningful to readers connected through Facebook, as well as some of the functionality the Facebook commenting system seems to offer. Something of a hard call – what do you think?