Of course they are all different, but I am interested in hearing other people's experiences with them. I just got a screening call to see if I'm eligible for one, but it does involve putting a camera into my lungs and taking a cell sample.
A friend of mine did one that purported to be studying sleep, but I guess he had to stay awake for as long as possible and he had to go in with a clean system-- no drugs (obviously) including caffeine or nicotine and definitely no alcohol. From what he told me, it was pretty miserable. No TV, no books, nothing.