This approach wouldn’t really scale well for a busy forum with deep and broad threads, at least not without some additional javascript to allow expanding and collapsing the threads, but check out fugi. Responses to the original topic are shown horizontally and followups to responses to the original topic are shown vertically below them. Sounds confusing I know, but check it out, it makes sense when you see it. I’d really love to see this enhanced with some ajax/javascript to allow for expanding and collapsing threads.