That's great. I tested logging in to Steempeak with my Facebook account. It worked fine. Commenting wasn't available, yet. But it will be soon.

When you're not logged in, you can't comment at all. It would be helpful if the UI directed readers who are not logged in to create a guest account when they pressed the reply button. The process of creating a guest account using Facebook/email/etc. already works fine. There's just some fine tuning to do when it comes to he user experience. @midlet is the right person to discuss these things with because he/she is a professional UX designer.