Amit Agarwal has noted that Google has recently begun indexing Facebook comments the way that more traditional, custom commenting systems have always done. This is bound to be good news for those who run sites and want to use Facebook comments but have avoided doing so because of SEO implications. One of the downsides of third-party, Java-based commenting systems including Facebook, Disqus, and Intense Debate has always been this lack of indexing, making discussions that happen within those systems far less valuable. With this change, it seems likely that Facebook will make even further inroads into domination of the commenting game, and that you'll have to be ever more vigilant about what you said and where.
Google starts indexing Facebook comments
Google has begun to index Facebook comments