One issue is that transparency makes discovering someone's salary easy, but discovering their value is still hard (at least for the non-employer). I haven't done all the math, but my intuition based on similar markets is that it would actually cause salaries to converge: high-quality employees are likely to get paid less, low quality employees end up getting paid more.

Which is a wonderful thing for the corporation. Self-monitoring and peer-pressure among employees. "Really Dan, you want a raise, how much more than Jim do you think you are worth?"

Suddenly, you salary is directly related to your boldness and the amount of flack you are willing to take from employees, not your talent or value to the company.

What about transparent equal salaries? Or at least equals base salaries and some kind of performance bonus.