Open the Terminal (located in /Applications/Utilities/ ) and enter the following line, followed by the Enter key:
defaults write com.blizzard.worldofwarcraft DesktopModeIsDefault 1
Once entered World of Warcraft can use your current desktop resolution as if it were the native resolution. In order for this to work, you must first set your desktop resolution to whatever you want World of Warcraft to run at, and then launch World of Warcraft.
To revert your preference file, issue the following command in Terminal:
defaults delete com.blizzard.worldofwarcraft DesktopModeIsDefault
You should make a backup of this file before attempting this, just in case. The file is located here:
To access the ~/Library folder, while in the Finder hold down the Option key and select the Go menu. You should see a "Library" entry - that is the ~/Library folder. This option is hidden until you hold down the Option key with that menu open.
This will allow you to use whatever resolution for World of Warcraft you choose like you used to without the added distortion/UI offsets caused by the non-standard resolutions that are now hard-coded into the game.
Warning: Using this method will also cause the desktop resolution to be at whatever you chose before you launched World of Warcraft. You cannot increase the resolution from outside of World of Warcraft and then re-enter the game's fullscreen mode, as this will improperly set World of Warcraft to the new desktop resolution. It is a tradeoff, but as long as you do not exit fullscreen mode it should suit your needs in-game.