My Fiance and I purchased the "buy one get one free" Serta Pillow Top Mattresses a year ago in late March, 2008. My fiance noticed right away his mattress was starting to sink where he sleeps. Gradually over the months he started to have a crater in the mattress and was having back & neck problems (actually needed prescription medication for his neck!) My mattress started to sink as well, but not as badly as his, at first. I have a queen and he has a king. Not sure if the mattress size makes any difference. We are not large people... read full review »