Ask HN:Facebook comments and SEO

Hi HN. Here is the small question, you have added to your website facebook comments, that's good a lot of facebook users are out there and you don't have to worry about much. But the comment system will be shown only to logged in users of facebook in a IFreame on your site, no problem here.

Now for the question, what do you think will happen for SEO? I am asking this because on blogs I have found my answers within the comments, but since this is an iframe with login on top of it, is google going to read it as part of your content or as facebook content?

I had this discussion with my partner about we should have any other login system on our website or only use facebook as login, we asked if we had more then 3-4 friends (active internet users) that don't have facebook.

I argued that we have around 1.5 billion internet users and have only 600 mil facebook users, so we should have the 2 login / sign up's, but then what about the comments? We should have a facebook comments system and a normal comments system, based on what the users is using as it's login, that again if we can figure out what the facebook comments will do to our SEO.

Thanks