I am currently leveling in Deepholm and I about 75% to 83.
I saw this blue quote on MMO Champ…
In terms of gameplay, our goal was to take advantage of the changes to the environment and use them to help address previous issues with quest flow. It was an opportunity to streamline progression within Darkshore so that the overall experience for players would be much smoother and require less running back and forth.
Leveling in Cataclysm will go faster as they are changing the questing design quite a bit and limiting the need to fly back and forth from quest giver and quest area. Some quest givers now actually allow you to complete quests at that location through a spiritual link instead of flying back.
How many night elves can look at that blue quote and remember all the running back and forth in Darkshore to level… it was horrible and really drug out questing in the zone. Low and High level characters alike will most likely benefit from the new questing linearity of moving through zones and it should speed up leveling. My guess is leveling in Outland will be the worst it will be as Northrend was a lot better than BC or Pre BC.