We have a tempur-pedic and love it. I haven't noticed it deteriorate, but just had it less than two years. Nor have I noticed it getting hot. We had heard about the heat issue and asked about this while looking. The sales guy said the newer designs have channels in them that let them breathe and 'eliminate' the heating up of the older models.

Only thing I've noticed 'bad' about it, is that if I get up for a minute or less and get back in, there will be a dipping feelilng between where I was before on the bed and my new position. Essentially, it takes a while for the foam to go back to normal after your body softened it, so when you get up and back down, the imprint of where you previously were is still there. It only last for a minute or so, and I don't notice it anymore, but I did notice it early on.