I've gone back to leveling my alliance toons a bit. I keep thinking I'd like to get at least one, if not more of my alliance characters to 85, especially given the emphasis that the new expansion seems to be placing on the conflict between Alliance and Horde, I'm really hoping for some difference in content through MoP for the two factions - certainly more than we saw in Cataclysm where it was mostly limited to a few quests in Twilight Highlands.
I've put leveling the Death Knight on hold until 4.3 rolls around to take advantage of the reduced leveling time through Northrend. So in the meantime, I'll try to get as many of my alliance toons to Outland as I can. It may not be more than one, but we'll see.
As a casual player, I was very interested to see what would be out there for me in the new expansion. I certainly like the idea of a new race and class to play, although I'm hoping Blizzard follows through with the idea of opening up more slots on any given server so I can continue to have one of each class on a particular server.
I think the new talent system will actually make leveling a little bit easier since it will reduce the points at which a decision needs to be made during the process. It seemed like at each phase, the decision you will be facing will be more impacted by your personal style and how you'd like to level rather than the need to pick any particular talent at each stage in order to be able to level effectively.
No longer having to train for spells will also be a huge time saver. Right now, in the quest path from 1-60 especially, there really aren't any points where you need to return to a major city anymore, so I can often end up going quite a while without picking up a new spell. Eliminating that will help a great deal. The only downside to this approach that I could see is if you're trying to level a profession at the same time, you'll have to return anyway. Scattering profession trainers throughout the world would help a lot with that.
I think the simplification of the weapons slots for various classes will also make the decision making on gear while leveling much more straightforward. Hopefully, Blizzard is able to take the time to tweak the quest rewards while leveling a bit to make sure there are enough wands and ranged weapons available for the classes that will now need those more.
Finally, the elimination of minimum range for hunters will make a class that already levels quickly even more formidable. Combine that with the ability to designate any pet as tenacity, ferocity or cunning, and you should be able to grab any pet you want and make it do what you need.