Blizzard is clearly in "troubleshoot the exp curve" mode, having expanded the amount of EXP required for levels 70+ by 80% in the most recent patch. This is almost certainly an overadjustment in the opposite direction (it was a bit too fast previously). Anyway, I was feeling concerned about getting poor Cheery stuck in a hole that I couldn't dig her out of exp-wise, so I decided to backtrack into Borean Tundra.
What's the damage?
I have one major subzone to deal with in BT, having cleared all of Howling Fjord and the first Alliance questhub in Western Dragonblight previously. This got Cheery to level 73. That's the good news. The bad news is that I hit level 71 prior to the exp nerf. Had I needed the extra 80% for the 70->71 transition, I would still be bogged down in level 72 as I moved into higher level content in Dragonblight. That's not entirely a disaster; I also started Northrend at level 68, which consumed about 1.2 million experience prior to level 70.
Taken collectively, my guesstimate is that a level 70 character entering Northrend now would hit level 73 if they clean out both starting zones. On the other hand, most players aren't going to want to have to complete every single quest in both zones, especially on multiple alts.
A growing role for rested Exp?
One of the quirks of the escalating EXP curve is that rested state experience is starting to play a larger and larger role in the game. In WoW (and subsequent games, such as LOTRO), characters accumulate a bonus that gives them double experience for killing monsters (but not quests, discovering geography, etc). For each 8 hours you spend logged out in an Inn or major city, 5% of your exp bar converts into rested bonus (to a maximum of 150%). In my experience, this bonus amounts to about a third of my experience leveling via questing at midlevels in WoW (one third is the base exp amount, and the last third is quest completion bonuses).
At low levels, this bonus makes you level faster, but isn't a huge deal. Moreover, it's easier to use it all up and get stuck with the regular rate of exp gain. Once Blizzard starts setting the exp for your next level at 2.3 million, however, the 15% of your exp bar that converts into rested state if you log off for 24 hours is over 300K. The good news is that someone who plays an hour or two a night no longer needs to worry about using up all of their rested state. Heck, I had to sign off early last night due to server instability, and I had more than enough rested state to carry me through a lot of questing today. The bad news is that, if you do somehow run out (or have to log out somewhere that isn't an Inn), you may have a harder and harder time making your next level.
Time will tell, and this won't be a problem for players who juggle a lot of alts with rested state, but players who want to burn to the cap for raiding/arena may not be happy.