Joel said in a stackoverflow podcast that he publishes the formula for the pay scales and profit sharing amounts so if an employee really wanted to know someone else's salary they could figure it out based on their position and how long they have been with the company.

I like the idea of transparency with salaries as long as the company pays well. If an employee decides he/she wants a higher salary than is afforded by a system like that they can look for another job or start their own company.