While I don't know anything about the latex ones, I can offer some second-hand opinions about the Tempur-pedics
My parents and my grandparents on my mother's side both recently got a Tempur-pedic mattress, and they've really been raving about it. My grandmother has had back problems and such for a while, and has said that she's slept better than she has in years on the new mattress.
My parents have also been quite saitisfied with theirs. They mentioned that on the first night, they had a really hard time getting used to it, but once they got used to sleeping on something that isn't a regular spring mattress, they're both sleeping quite well.
I had a chance to check out the one my parents got on a recent trip out to CA, and it definitely is weird. When you first sit on the thing, it feels like you're sitting on a concrete slab wrapped in felt. Initially there's very little give, but you slowly sink into it, and it starts to feel more comfortable. As it was my parents' bed, I didn't actually get the chance to sleep in it, but I can see how they'd be pretty comfy.