Facebook would own other site's comments. Not good.
it seems like the widget already allows for people without facebook accounts to comment
Something similar to what happens with users who want to comment but choose not to use Disqus, methinks.
I'm sure that this Facebook system could be hacked to allow for unregistered comments.
2) As plausible as hacking Disqus to allow Hacker News accounts.
Hell, I am far more concerned with how much credit agencies seem to know about me, and I never like giving my information to them =p.
How will you feel when your credit rating gets lowered because of some off-hand comment you made on some blog?