I think a few people have hit the nail on the head here. Nobody wants the flaming, but the section has a purpose which requires proper moderation and guidelines to come to its fullest potential.
First, I think the name might need a change. The fact 'complaints' come before 'compliments' sticks, and I must say I tend to always think of it as the company complaints section. Moving the wording around, or maybe naming it something like 'Company Experiences' or 'Company Support Stories' might move the negative connotation away.
Second, proper moderation is a must. I can't say I really noticed any of the topics that bring out this supposed worst, but I think keeping stuff on topic and keeping users from unnecessarily emphasizing the same aspect again and again in a negative context (while not detailing their personal experience with the company) should make a big difference.