I don't know - it's just seem so expensive. Looks like a luxury to me, not a necessity - in the UK the trainers in my gym are 40quid an hour, say you see them twice a week it ends up costing you 350-400 a month, that's boat loads of money, way outside the realm of affordable for most people.
Also, the ones I've seen so far (when I peak at them while doing my own workout) seem to just act as spotters, and give basic tips you can get online for free.
I'd love to be wrong though - I've considered 'giving it a shot' myself, but I still need some convincing.