Since I'm still leveling to 80, I'm focused more on how I'll be tanking endgame content in patch 3.1. As you've likely heard, gorillas will be losing their signature ability Thunderstomp. Instead it will be merged into the Tenacity tree, where any tanking pet can pick it up. As bears already have Swipe, it seems to me that bears are going to be the overall best choice for multi-target tanking, as well as being a nice tank pet in general. So that's what I've gone with, a brown bear named Artuir.
Hm, says you. A tanking pet? Wasn't Gweryc the one tanking before? Yes, but sadly, that was before. The Lich King took the survival tree out back and beat it with the ugly stick to the point that there's no hope of looking to it for melee. There's entirely too many wasted points over there to get to the good stuff. All I'm left with is Beast Mastery. That's the point where I had to ask myself, what can I do as a beast master that still offers value? I can't dps competitively, I can't heal, I can't CC or decurse or anything niche. But hey, I can still tank. I just have to serve as an intermediary for the pet, I guess, as he fills the role of tank instead of Gweryc himself.
That said, I've got to gear different and think different. (Yes, I own a Mac.) Where I was using TankPoints before to increase my personal survivability, I'm now looking at gear in terms of Effective Health. EH is calculated using armor and stamina, both of which -- unlike defense, parry, etc -- are stats that scale toward my pet. The greater my own EH, the more damage Artuir will be able to soak up.
I'm a little worried about his threat generation, though. If I gear exclusively for survivability I won't raise my RAP, meaning I won't be contributing to Artuir's own AP, which in turn boosts the threat from his Growls. The TankPoints implementation of EH also includes Agility, so I may follow a rule of thumb that I itemize according to the gear with the highest level of EH that also includes Agility.
As I set about my new life as beast master, I can at least say I'm in good company. Big Red Rhino has been covering tenacity pets as tanks for quite a while now. Hopefully I'll have a new accomplishment to add to their Feats page one day.