If you know what your coworkers make, you have a better idea what you can negotiate up to than if you didn't. That's true even if you can't go into a discussion and name names and dollar amounts that you know.

If a coworker told me their compensation, I would not reveal that in a discussion about my own pay. I hope that the reverse is also true. I think it's a mature and cool-headed position to have. Not everybody is mature and cool-headed though.

I have also heard the best way to get a raise is to move companies. I like my job though.