Every mattress needs to be rotated. You do this to maximize even wear and enhance longevity. Rotate your mattress every 3 months. If there is a large difference in weight between the two people using it, do it more frequently...as you see wear patterns beginning to form under the heavier of the two of you.

I think you should also consider the warranty. If it covers loss of firmness or depression, at which point? If it allows for small depressions don't forget to rotate it.