No nesting. Is this 2004? How are you supposed to follow a conversation more than two posts deep? This is PHPBB with more javascript.
Turns out people are actually very, very good at following a conversation. They hold the state in their heads. Try going to a bar and sitting at a table with eight or nine people at it. If you could write a transcript you'd see the conversation spiralling, branching, merging and branching again. And nobody gets lost. All a forum has to do is record who said something and in what order. Threading is a ridiculous "solu…
Say a newcomer joins the conversation (at the bar) halfway through. He is missing a lot of context. His kind friends would then fill him in, unlike the internet.
A threading like structure however, allows you to quickly scan the parent, and if need be the parent's parent. It's within the user's perogative to choose how much information he needs to be caught up.
That being said, I'm very open minded about seeing the new approach develop. Heavily nested threads are a far from perfect solution.