Overall I think it is better out in the open. Even when it is hidden, people find out and then are angry, resentful... and it can lead to apathy or even sabotage. When salary and reviews are in the open, they can be questioned and, if needed, corrected. It makes it a lot harder to play favorites.

Salary discrepancies aren't just based on gender. I have been told, more than once in a review that my work is excellent, my work ethic is outstanding... no negatives, but in the end no raise, when confronted the answer was "You don't have kids, so you don't need the money. John Doe is divorced and has 4 kids."