We bought one - a California King size, 3 inch thick model to place on top of our "regular" mattress. I've had 2 lower back surgeries, and normally find it difficult/impossible to sleep without constant twisting and turning to find a comfortable sleeping position.
The memory foam mattress cured all that - and I now sleep for hours at a time with no need to change positions - and wake up FAR better refreshed than previously - liked it so well that we bought another, 4 inch thick queen-size version, to replace the mattress in our RV - and like it equally well for all the same reasons.
A simple and common moisture barrier liner between the bottom sheet and mattress cures any issues in that area - and the summer/winter issues have been non-issues for us. We bought ours thru
Overstock.com: Online Shopping - Bedding, Furniture, Electronics, Jewelry, Clothing & more , and they each were under $200...
I highly recommend them - in our case, they have been FAR better than the past standard, high quality mattresses and water-bed mattress we have tried to help with our back related issues.