On my blogs I'm seeing comments in moderation that have www.bing.com and www.facebook.com in the URL field. I've been scratching my head trying to figure out why a blackhatter would post scrapebox comments with those links. Is it not a waste of time? The comment doesn't have a link in it either. Is there some theory that posting links to bing.com or facebook.com somehow increases the PR of the blog they're posting on? I believe I saw an SEOmoz study on external linking, where they found that linking to google.com was negatively correlated with rankings. But linking to microsoft.com was correlated slightly. Is this perhaps what they're thinking? Perhaps someone on here who is actually doing this can reply with the reason? If it's something not well known, could you pm me please?