babelfish LIED to me.

I'm used to that, though.

In particular, I think forums shouldn't use comments. Instead there should just be forum posts. You start a new topic with a forum post and you reply to existing topics with forum posts.

This ensures that the UI for posting is the same, whether or not you're replying. This is really important for permissions, administration and user experience. Right now, with the comment system you simply cannot hide the fact that comments and nodes are fundamentally different, have different features and a different look (particularly on data entry). It's also difficult to administer comments because they're a different node type.

The queries to find new posts in a forum are horribly inefficient because they have to check comments and they have to check nodes; also, comments don't have individual 'read' states, but nodes do. So if you touch a node, you've read all the comments, even if there were 5 pages of comments that you haven't seen.

Comment navigation is absolutely horrible, especially when you combine paging and threading. It's hard to go back and find new posts with the threading, and with paging it's hard to link directly to new comments. All of this is actually quite easy with nodes because each node has an individual read state. You can have a 'new' operation which figures out which node is newest in the topic chain and starts there (or maybe a topic or two before it so you have some context).

Fundamentally, though, I think forum posts and forum replies are the same data, and the difference between them is that a forum post is a reply to nothing where a forum reply is a reply to something. If you change a forum reply so that it's a reply to nothing, it is automatically promoted to being a forum topic. That, I think, is a very important distinction.

Note that I think blog-style comments are probably well served by remaining, simply, comments. They don't generally need the kind of added features that forums do. That's an important distinction as well.