LOL, I guess you'll be reading that other link I recommended sooner than expected.  Typically, the gamma setting for MACs is 1.8 even though the accepted standard for monitor calibration stands at 2.2.  Two new MAC's at work still had Gc set to 1.8 thus the brighter screens.  I immediately corrected that little issue.  I would recommend calibrating your monitor to gamma 2.2 predominately because that is the accepted standard for the internet.  Especially if you post your renders in the gallery.  Resetting the gamma node in VSS to meet the requirements of your monitor is fine if you are only viewing your renders on your computer.  But if you plan to post renders on the web, then you will need to keep the VSSProp as is and change the gamma settings for your computer set up.