Ten or eleven years on here: have I think a bit more than a year left on the 12-years warranty. Looks brand new. Nothing has moved. When it came, there was a booklet (or a PDF?) explaining how to set it up: took me 30 minutes to set it up and since then, I never had to change the settings once.
It's not suitable for people used to cross their legs then and kinda sit on their legs (I had a roommate doing that).
The most common complain with the Aeron is that the frame pushes too hard on the back of the thighs but I don't get it: too me it's an improperly set up chain as I'm only in contact with the (amazing) pellicle mesh.
I love that chair. In the US it's very easy to find refurbished ones as good as new at a big discount. In Europe it's doable but not at easy.
If that chair dies before me, I'll immediately rebuy one.
EDIT: a "trick", I think explained in the official doc: the recommended setting (but you do what you want) is that the chair has to lean back if you put both your arms behind your head and then lean forward again when you extend your hand in front of you (for example reaching for your keyboard).