I bought one form them in 2004. It saggs in the middle and I have had them come out twice to see it. I can't sleep on it without rolling to the middle.
I change my sheets once a week and always turn my mattress when I change sheets. I flip it, then flip it again, then flip top to bottom then flip it again so I sleep on all areas. When I am in hotel beds, etc I sleep along the edge of the bed, but this bed got a dip in it from when I was going through CA treatments and spent alot of time in the middle of the bed watching TV.
They take the sheets off and measure the dip in the mattress and if it is more than a certain amount they will replace it. Of course the dip isn't as noticable unless someone is on the mattress, it will puff up when it is empty, but they don't care.
I am about ready to get a new one and I will not go to Sleepy's again. I took the insurance coverage for nothing. I don't think 4 years is long enough to own a mattress, and I started calling them when it was 1 year old.
Also, if you have so much as a pea size stain on the mattress it negates the warrenty. I have twice cleaned my mattress with my little green machine before they showed up because even though I have a mattress pad and always have sheets on it somehow it gets spots on it, maybe from turning it, greasy fingers or something.