Padding
I was flying on a 767-300 last year and in the old economy seats. IMO they are much more comfortable than the new hard seats.
What is up with airlines and the elimination of padding in seats? BA Club Europe seats are the last bastion of padding I have found. Of course there is a weight saving but a little bit of foam makes a difference. My desk chair here at work has more padding than a Qantas economy seat.
(This has happened on the MET train system in Melbourne where they replaced the comfy seats with anti-graffiti seats which are uncomfortable. I don't see many aimless youth wandering around Qantas Jumbos with Stanley knives though.)