I don't do the "lets re-negotiate my salary" bit, it's up to my employer to keep me at or above market rate for my skills, I shouldn't have to ask for it.
And given the fact that this market rate is not a clearly defined value (also thanks to employers' reluctance), don't you think it is necessary to at least negotiate with your current employer if you believe you're being paid below par?
That being said, if I wasn't privy to this information it wouldn't take much to find out what the other people on my team are making. I don't think I've ever worked in an environment where salaries were considered top secret information.