There's a lot of concern that levelling is too fast in Cataclysm. I am not sure if it is too fast or not, but lately I've been making a bunch of low level alts. Here is one thing I've noticed about levelling speed.
If you do nothing but quest, the XP curve seems to match the quests very well. But if you do anything else like a dungeon, or some PvP, or even herbing/mining, it feels like the XP from those activities starts making you outstrip your quests.
It seems like Blizzard wanted to make running instances, running battlegrounds, or herbing/mining viable methods of leveling. So that questing wasn't the only path. But to me it feels that if you dip into multiple areas, it hurts questing because you get pushed past the optimum level for the quests you currently have.
In Vanilla, questing was the sole means of levelling. Dungeons formed too infrequently to really affect you. Battlegrounds didn't grant XP. And herbing/mining certainly didn't help you level.
(As an aside, I don't really understand why herbing and mining started granting XP. That seems so unnecessary to me.)
I don't know how one would fix this issue. If Blizzard expects someone to do multiple activities, and adjusts XP accordingly, then someone who just quested would find themselves under-level for the quests they were getting.
So that's my observation on the state of the early game and leveling speed. I'm not sure how extensive the problem is. I have a low-level rogue, who has quested, done each available dungeon two to three times, and is a herbalist. That rogue has definitely out-leveled her quests. On the other hand, I have a low-level shaman that has done nothing but quests, with no professions. That shaman matches his quests correctly.