Clare, I have a friend who's husband is a chiropractor...he absolutely swears by them and recommends them to his patients. He said that they can be expensive for the better ones, but well worth the price paid.
Personally, I tried one and I didn't care for the ooshy squooshy feeling - I just love down pillows.
But from the standpoint of being better for your neck and alignment...he said that nothing beats them!