This site has been so helpful to me that I thought I’d contribute just a bit. I cannot really offer much in terms of scientific analysis, only my impressions.
I live in New York, so went to the Casper showroom. It’s someone’s swanky Noho loft and the owner’s actual bedroom is being used as the place to try out the mattress. The rest of the apartment is a start up - long tables full of Macs and 20-somethings. They are moving, and everyone is incredibly friendly and helpful.
The mattress itself - if you sit on it’s edge, you literally sink into it - it is very soft. Once you lie down, it acts as a memory foam bed - if it’s your thing, that’s great, but a latex mattress it is not. Soft, exactly like a high end hotel bed.
I ended up going straight to Scott Jordan’s furniture and paying double the Casper for a Berkeley Oslo mattress. The guys over there are great as well.