The girlfriend has one.
She has back problems (her muscles are too strong for her hacbk, so she doesn't have a curved tail bone). Although she has "back problems" it doesn't affect her too much (normal movement can do everything she wants to do, sports e.t.c) it's just that with a matress with loads of springs, it does get uncomfortable.
I quite often share her double bed, and the matress is really something special. Not too sure which one it is (think it's tempur) and think they are fantastic to sleep on, really comfortable.
So comfortable infact, I prefer to sleep in her bed, then my own springy matress one !