We can't live without it! I have degenerative disc disease, and my 6 ft 9 husband who travels for a living wouldn't be OK. We call it overnight back repair.
We called Tempurpedic about the heat issue before we moved here 4 1/2 years ago, and asked them about putting a quilted type polyester mattress pad on it. Although, they don't recommend it, they said, "whatever helps to continue using it in a therapeutic way". We got a very fluffy cover from Linen Source (and just changed to our second one), and it's fine. It has to be washed and line dried at Nellies because our washer isn't big enough.
I think new Tempurpedics might be better with the heat, but not sure. But we can't live without ours due to medical reasons...it really isn't a luxury.