I've jumped into leveling my Priest(up to 23 now, woo!) and it's a decent amount of fun. I went Shadow first, got bored, went Disc. Holy Fire is just too awesome to not be priority, so I just Holy Fire -> Smite -> Smite -> Wand(got the blue wand from BFD which is made for late 20's early 30's but has no lvl req so is way OP :D).
But my focus is more level 80, I figure in a week or two I'll be there pending play time and if I get on my Mage at all or not.
For Priest I have NO idea on stat priority.
So....
How much Hit do I want for my Shadow spec?
Do I ALWAYS prioritize MP5, Haste, or Crit as Disc?
How much Haste vs Crit vs SP for Shadow?