When facebook first rolled out their feature where you could reply to comments I was disappointed. Only one level of nesting? I was used to reddit-style commenting: each comment indented under the comment it responds to. But I've changed my mind after seeing how well single-level nesting worked with the 200+ comments yesterday, and now I think it's a great setup for discussion. I just had to change how I was thinking about it.

What happens when you can reply one-level deep is that each top-level comment provides a topic and a jumping off point for a discussion with back-and-forth. In yesterday's comments we had simultaneous discussions on loosely coupled topics without them interfering with each other, and each of those discussions felt coherent.

In a massive discussion you would still have a problem with needing to break things down further, to get sections of the discussion small enough to talk in, but with the size of interactions I've had on Facebook one level of replies seems like a good fit.