Personally, whilst I may be a grumpy old sod, I do favour making friends with my fellow employees and getting to know people's salaries after a drink or two. Yes, it goes against terms, and I think an 'I'll show you mine if you show me yours' is the only approach. This means obviously trying to avoid such discussions with the type of person who will blab about the discussion. However such data is generally helpful when negotiating - and I would never say 'Oh, X gets Y so I should get Z' - simply to understand where you are standing and whether it seems reasonable with respect to your relative contribution.