Leveling seems to be just as fast or faster in wotlk than BC was when it came out, regardless of the extra XP. I played a few hours today and got half way to 71 just slowly doing quests and exploring. I don't doubt people that popped some energy pills and stayed up all night and day to level would easily be able to make 74. There are many people on my server claiming they started playing last night at midnight and only stopped to sleep for a few hours (sad as this is).