I have osteoarthritis in my lower back and hips, and for a variety of reasons can only seem to sleep on my back, with the end result being that I would always wake up in pain; my dad suggested that I try a memory foam mattress topper, since his had worked out for him, so I ordered this one.  I've been sleeping on it for a week now, and hallelujah!  I can get up in the morning without my lower back killing me!  It's not perfect, mind you (there's still a bit of a smell, although not nearly as bad as other foam items I've used), but it's made an immense difference in how I feel when I wake up in the morning, and it doesn't seem to be overly hot, either--I have it underneath the bottom sheet and a mattress pad, which may help; it should certainly help keep it clean.  Now if I can just get used to my mattress suddenly being 3" higher...