My tanks always started out as a DPS spec.
I run overworld content with a few friends maybe 2 or three at a time, but usually just me and one other doing story quests, or side quests leveling new toons from 50-60 etc.
WHen they need a tank to help them through stuff I switched my tanks to the tanking spec and tried it out.
Warrior - I like it!
Paladin - nice! I like it wish the cooldowns were shorter.
Monk - uhh… stagger is a lil confusing… and all the brews…?
DH - 2 button rotation… Its okay I guess… still feeling it out.
Druid - I guess just swipe as much as possible and ironfur when you got to? still feeling this one out as well.