With the changes in patch 2.3, players won’t have to put off Razorfen Kraul, Blackfathom Deep, The Stockade, or Gnomeregan for later levels as they will be able to go through them throughout their 20s and roll into their 30's where Scarlet Monastery, Razorfen Downs, and Uldaman await to take people into the 40's and so on. Blackrock Depths is getting improved as well. I recommend checking it out the PTRs when they are available for patch 2.3.
Don't forget all the hard work from the Steamwheedle Cartel in Dustwallow Marsh which will give a big boost for the level 30 range too!
The original posts in context can be found here.
http://forums.worldofwarcraft.com/threa ... 16&sid=1#1