Through my favorite comment system ever, Disqus, I have enabled Facebook connect. If you have a Disqus profile, you can still use that. But if not, you can comment using your Facebook profile as well.
One of the main reasons I like Disqus is that I’m lazy. I didn’t want to manually add Facebook connect, I wanted someone else to do that for me. Disqus made it as easy as I think it can be. Yeah, I had to create a Facebook application for each blog that I run, and copy and paste keys into my Disqus page. But that’s a Facebook issue, not a Disqus issue.
There seem to be a couple bugs, so let me know if you have any issues. But overall, easy & simple. Well done to the Disqus team.