First, he doesn't find it comfortable; apparently this is not entirely unheard of, and a very good reason for buying it from Tempur as you can have for some time and then send it back if you don't like it. We bought it from a bed shop down the road who gave a 10% discount but no return policy.
Second, he says you don't get that lovely feeling of cold sheets when you move a different part of the bed. Actually, I think you do, but what do I know?
Love love love it. I was very sceptical about buying one as we had the pillows and I didn't like them gave me a sore neck but DH insisted and apart from the still annoying 2 yr old DS disturbing my sleep its the best nights sleep I have ever had. Super comfy and I now use the pillow too with no sore neck. Definitely worth the money.
As an aside, definitely not worth buying a Tempur mattress for children. They're not heavy enough to benefit for the body moulding effect and kids generate quite a lot of body heat and Tempur mattresses can be a bit sweaty making.