But before you get all angry about Blizzard wasting all that time you spent leveling, realize that things will likely even out in the end. Even though you'll lose 600,000 XP from the amount you have, you'll still be halfway through level 59, and you won't need as much XP as you did before to level to 60. So you haven't really "lost" anything, because even though Blizzard has "taken away" some XP, you didn't need what they took anyway.
As we've said before, these leveling improvements are going to be great news, not only for altaholics who are leveling up their third or fourth character by now, but also for guilds eager to see some new 70s to bring into the raiding mix. Folks who are leveling both before and after patch 2.3 are going to experience some strange math, but that happens all the time anyway (did you know that all the stuff you're killing at level 70 now doesn't count towards the experience you'll need to earn in the next expansion?). Blizzard is tweaking the numbers, but the experience will still be faster.