SCS allows you to rate people in game (up / down). It keeps track of who you enjoyed interacting with and who you didn't, then puts related icons :) or :( next to their nameplates, names in chant, tooltips, and in the LFG window.
Eventually the addon will pool data with your guild mates and allow you to share this data, though your ratings will always overwrite your guild's collective rating.
WORK IN PROGRESS