Hey Pokie - nice choice for a topic. It's early here, so I can only think of a couple things right now.
Sphag - I don't use this much, but when I do I check the stuff often - maybe every 6 months. It doesn't break down after that short of a period of time, but it does seem to pack down even if it started out fluffy. Just my experience - maybe I water too hard.
Osmunda vs. tree fern - I know there's a difference, but can't remember. I grow a few things potted with chuncks of tree fern and love it. I was going to ask the question of why this stuff doesn't seem to break down? Mine looks perfect yet even after a 1 1/2 years.
Lava Rock - I might just post another picture of something growing in this. So far, so good.
I know one person who is moving a lot of Laelias to pots of 1 inch granite pieces. You know Yoshi? I could see why this might be better than lava rock since it wouldn't absorb salts. It would be a lot heavier though.
It's funny how some people absolutely hate certain mixes and others love the same ones. It really does depend on your conditions, how often you repot, watering habits, etc. For instance, most people seem to hate, hate, hate Schultz's Orchid mix. I don't mind the stuff at all. In fact, before I got rid of almost all my phals that's what I used for them and they grew really well and had great roots. All those little pieces of rock in the stuff works for me.
Need coffee now. It's 5 am.