We checked them out and frankly found them to be a little bit too "form fitting" or "squishy" for our liking. (both for sleeping and sex)
We ended up getting a high-end foam-latex mattress, and then adding a memory-foam "slip cover" type thing to it.
I'm NOT fan of the memory foam mattresses as they' are WAY too soft for me, but I've got to admit, the memory-foam cover on a nice firm foam-latex mattress is FANTASTIC !