i have no problem thinking all these thoughts even without [ or may be precisely because of not ] knowing other people's salaries :) Knowing other people's salaries would allow to stop my imagination run wild about their huge salaries (while i'm getting peanuts :) and may be turned my thoughts into useful way, like for example :

"Joe earns 25% less than me, yet shows up at 10:00 - 2 hours earlier than me - may be i should start busting my ass a little bit." ( and if he does happen to earn 25% more, than, well, nothing lost and changed :)