Wow, that's interesting. I agree with Phyl, if I were asked to fill out one of those forms, I'd toss it in the trash as I was making my way, quickly, out the door. As Dr. Phil says, "people who have nothing to hide, hide nothing". If my doctor was so worried about my saying bad things about him, he should probably make sure he's doing what I'm paying him to do in the first place and following that Hippocratic Oath he had to take ("first do no harm", etc).
I would like to think that most people aren't going to judge a doctor solely by what I say about him. I used to work with a doctor who was just a mess - he looked like an unmade bed most of the time - ugly tie, shirt not quite pressed and tucked in, messy hair, but he was an excellent doctor. So hopefully my mentioning the fact that he looked like he slept in his clothes wouldn't damage his practice as long as he had built a respectable reputation with his doctor skills.
But if someone had a legitimate complaint about this doctor, hopefully there would be a complaint on file about it with the AMA (or whatever country you happen to be in) and that is public record. I can find out about the lawsuits or complaints against that doctor, which would speak to me much louder than someone casually complaining about him. Maybe the doctor should be more worried about that information damaging his career.
Does the 1st Amendment (Freedom of Speech) apply to internet postings? (US again, sorry - don't know about other countries..). I would think that if I'm not falsely accusing or threatening in my post, I should be able to express my opinions. I think we each have a responsibility to evaluate the opinion of others - just because I didn't like a particular doctor doesn't mean he's awful and no one should trust him.
Am I rambling again? This all makes sense to me in my head, but I'm afraid it doesn't when I actually type it....