I suggest adding an Add Private Notes feature for individual posters. It would work like this:
You click on a poster's name then click 'Add Private Note' and add your note. Now whenever you hover over that poster's name your notes for that poster popup in the tooltip.
Examples:
Poster1: Tooltip-> 'Maths professor'
Poster2: Tooltip-> 'Cool guy, makes intelligent points'
Poster3: Tooltip-> 'Entertaining read'
Poster4: Tooltip-> 'Professional troll, do not respond to his posts'
And so on and so forth.