Lead content designer Cory Stockton, aka Mumper, recently Tweeted that the cost to train Pet Battles has been reduced. [source]
"Just hotfixed the cost of Battle Pet Training to 10g. We still don't want newbie players but 100g was obviously overshooting that goal."
In addition to this hotfix, developers have addressed the Tamer dailies not resetting. [source]
"We found the bug with pet battle daily's not unlocking. It's been hotfixed and they should work now, cross faction. Thanks for the reports!"
He also clarified on how to complete the Taming Azeroth achievement. [source]
"Another note on pet battles, Taming Azeroth achievement is setup to complete with either Taming Kalimdor or Taming EK, you don't need both. Note that the display is wrong in 5.0.5 since the change was made via hotfix. Functionally, it will work though. UI is fixed in 5.1.0."