I've long been of the opinion that it's a good idea to hop from Azeroth to Outland at 60 instead of 58 and from Outland to Northrend at 70 instead of 68 due to the fact that I'd have some extra talents and skills in my repertoire and also be at a higher level compared to the mobs I'm killing.
With my priest, I've reached the point where I became tired with the old world instances, quests and quest rewards so I decided to take him to Outland as soon as he hit 58. Though I can't run Outland dungeons just yet, though flying won't be available until 60 and though not all quests are available, it was a very good choice.
As I write this, I'm 59 going strongly on 60 and I've already got 3 good gear upgrades from quests. There's a world of different (forgive the pun) between Azeroth and Outland/Northrend in terms of quest design and rewards. Quests are quick, grouped together in the same area and rewards are meaningful. It's a good thing they're revamping the Old World in Cataclysm. I'd go crazy if I had to level just one more character through there.
Speaking of flying, remember the days when couldn't learn flying until 70? Good old days - not.
Patch 1.0.5 commentary
4 years ago