So far on my little undead warrior tank I've tanked all the lowbie instances with great enjoyment and success, with my friend playing a holy priest (my very own pocket healer!). I was pretty nervous initially about Blackfathom Deeps and Gnomeregan, because I know I've gotten lost in there once or twice at 80. And we just opened up the Scarlet instances. We've done Graveyard, Library and Armory so far and they haven't been nearly as bad as I thought - even when a fleeing mob grabs the next group, no one is low on mana, I have lots of rage...really it just saves us time! (I am apprehensive about Cathedral still though.)
But Razorfen Downs. *shudder* I may have found my new nemesis.
I've ran RFD twice so far, and while both ended up as successes (no wipes or deaths) it's been harrowing. I'm not sure why, but I find myself rage-starved, lost in the giant maze, constantly losing aggro to DPS (maybe they just got AOE spells are are using them too early?) and worst of all, I keep getting silenced, so I can't taunt the mobs back either.
And the debuffs! Diseases, curses, you name it. And a freaking 15 minute curse? A BAD one, too. Horrible!
But of course, the worst part is the mob packs and how tightly grouped they are. I think every other pull was a triple-group pull. Sometimes a patrol would wander by and join in, sometimes a DPS would aggro a new pack just by running into melee on the pack I was tanking, etc. It's just chaos. Plus every group has a caster of some sort, and it's terrible for LOS pulls, so there's that extra headache to deal with.
The worst part is, it's still orange in the instance queue, so I'm sure I'll be seeing a lot of it in the future.
Sidenote: something I really love about SM is all the nice square corners for super easy LOS pulling. Plus, nice tight doorways and such to gather them all up, and even crates and cannons and stuff to back up onto for high vantage points/amusement! SM rocks.