I like the threaded view when viewing the titles of the posts but much prefer the flat when viewing the posts because you can read all the replies at once.
I fail to see how anyone would want to be switching back and forth to read the posts like we do on the old forum, when you could instead just be scrolling down and reading them all on the same page.
But it really is nicer to see the 'opening' page of the forums with the threaded so you can see if anyone has replied to something you posted. Sometimes you want to go back to the same post and keep reading all the replies but often you only want to go back if someone has replied to something you posted as it may contain a question for you, or comment you were waiting for.
Also, I cannot find the difference between threaded and classic. Is it really subtle? Or am I missing something obvious?!? Can you point out the difference to me?
There is much about the new forum I really like. I think it's an improvement on the old and I also think it's not so much different that the old forum diehards will find this difficult to switch to.
I look forward to the switch-over so that we can all be on the same page, so to speak.