Since getting into the World of Warcraft: Wrath of the Lich King Beta Byron "Messiah" Mudry has been flooded by questions about it by friends, guild mates, and just about everyone else. Everyone wants to know about something in the beta, whether it is how a Death Knight plays, which professions should they level, who is best in PvP or any number of other questions. However the most often asked question is "What's it like compared to the Burning Crusade?".
Congestion in early zones led to quest competition Everyone was competing for the same resources and kills and this lead to frustration, delays, and eventual griefing between players. In an attempt to minimize this in WotLK, Blizzard separated the starting areas for each faction in each zone a little more, and added additional faction quests that focus on different resources and kills. They also added what seems like many more quests in each zones and broke them up into many more small quest hubs. This also makes questing far less frustrating as you very rarely need to run across a whole zone to turn something in. You get to a small quest hub, complete quests near it, then move to the next one.
You can read all about it in Messiah's Editorial - Comparing Wrath of the Lich King to The Burning Crusade.