To make gathering feedback on multiplayer maps easier (for dedicated server owners, as this isn't send to the db) you can [Up]vote or [D]ownvote your favourite maps. To do this, use the Q-menu:
Press 'q' (quick menu) then 'm' (menu) then either 'u' or 'd' (up/down). A message will be displayed. At the moment it's up to dedicated server owners to parse their log files for this, since each server has their own rotation.