I don't tank bosses much; our raid leader is a great protection warrior and he tends to main tank them. Which is fine by me since I like to DPS too, and for bosses that crush it makes more sense to have a warrior or paladin tanking them anyway.
But as a change last night I main tanked Azgalor, the fourth boss in Mount Hyjal. Honestly, it was awfully boring. Stand in one spot waiting for the mob to be misdirected to you, then hit it a whole lot and hope the healers can keep you alive. I managed to screw up even that simple thing; I was moving around a lot trying to dodge the Rain of Fire and made it tough for our DPS to stay in a good position while avoiding his cleave.
Azgalor doesn't crush, so he's a good match for a bear tank. The thing that makes the boss tricky is there's a frequent zone-wide silence. You need lots of HoTs rolling on you to survive them, and you want to keep your few long cooldowns available for crisis moments. Sadly I only have two: Badge of Tenacity and the Frenzied Regeneration. I really hate not being able to eat a healthstone. The clever thing I did was stop attacking entirely for the last two minutes of the fight. Bear threat is great; I was doing 630 dps through the fight and got so much threat that no one could catch me. No attacks means no parries and no parry gibs, the damage I took was a lot less frightening once I did that.
The other half of tanking Azgalor is tanking the Doomguard adds. That's a lot more fun because it requires moving around, kiting mobs to NPCs, quick pickup of threat on adds, and if you run two tanks you can swap to DPS during the fight. Nice workout.