QuestJunkie has two functions. First is a barker for when you complete a quest objective (settings are in the Interface Options Panel)
Second, QJ also allows you to browse the quests of anyone in your party that has QuestJunkie installed on their computer as well. Open your QuestLog to access this.
QuestBarker has been renamed to QuestJunkie. Look for other addons by me with the Junkie name :D