I don't care for nesting much either. While it may be more like real life one-on-one conversations, I find it more difficult to follow an entire thread and very hard to scan through. I can enjoy a segment, but that's one of the problems I see: it segments a conversation greatly. I think things stay more on topic with a flat discussion, and I discover things I would have missed in a threaded one.

I'd love to see some innovation in the forums space, it's been a while. I still don't see it, but I'm hopeful.