Beast Mastery is good for leveling. Don't bother spamming Arcane Shot, it is a mana hog. Use Serpent Sting, auto-shot and let your pet do the work while you alt-tab read something lol. I play my hunter in windowed mode.

If you're up for risky stuff and have uber reaction time, Beast Mastery is good for PvP too. See http://www.warcraftmovies.com/movieview.php?id=35344