Paul1977:
Up, but with modern mattresses flipping isn't an option since they all have pillowtops. I'm heavier than my partner, so all rotating has probably done is make 2 even dents instead of one big and one small. We both just sleep in our grooves now!
If it's a guideline in their warranty documentation and you haven't followed it, then they are likely to be less excited to just drop a new mattress on your bed for you.
I'm not saying it would get refused outright, but it's a factor. Some types of finishing products do build memory over time.