God so much has changed. Back in BC i levelled a rogue to 60 and burned out on all the grinding. Couldnt face the thought of it one day and didnt play for a year.
So I retried it late stages of wotlk and well now you can level through doing almost anything. Most importantly get rest xp, every time you log out do so in a major city - thats 2x xp gain. the xp requirements to 70 have been lowered. You get xp from gathering, completing quests (10 kills max for most), PvP BG and a huge amount for running a dungeon (using the dungeon finder you flag yourself Looking For group and keep on doing what you were doing. When 3 DPS a healer and a tank are ready youre taken to the instance, and plopped right back when finished. Same with battlegrounds).
Add in a good questing addon (paid or free) and you fly through the levels. Levelling my mage, I would follow the addon for a bit, play a bit of pvp and run an instance and I would ding and have to reset the addon because I was way ahead of it. basically its just a lot more fun now and Ive got an 85 fire mage and started on an alt even though I only play casually.
Of course, there are those who say its ruined the game, that you dont 'struggle' or 'earn' your levels. But for me, itds made a far more enjoyable game. Cata really added the icing.