Here's some of my experience as a quad boxing shaman.

I usually roll with a tank 4x ele shammies in pvp gear, the following list I can do with any tank, even green geared ones.

Slave Pens
Botanica
Ramparts
Mana tombs
Mechanar (might want to skip the +- boss, altho, he's still quite doable.)
Blood Furnace
Sethekk Halls (I can 4 man Sethekk easily even.)
Underbog (tank with 12/13k prefered, otherwise bosses are easy and trash is definatly overcomable.)
Steamvaults


The harder instances are (from least to most tough)

Shattered Halls - It's not that hard with a warrior tank, I cleared it well within the execution time limit with a warrior tank once. But I can imagine it would being well hard for any other set up. We pulled everything far back and used fear on each pull. This worked like a charm. No wipes, nice and swift. But without fear or an ubergeared tank, I might postpone doing this one. The least tough of my tough instance list.

Arcatraz - I've not yet done this instance succesfully, but I also admit I never gave it a good try. With some pots and such, it's no doubt doable, but definatly among the harder ones. But not the hardest.

Shadow Labs - Doable, but unpredictable on the second boss. Need some extra macro's for Murmur as well, altho he does die quite fast. Only did it once myself, didn't bother doing it again, was well annoying, really, + some wipes on second boss.

Magisters Terrace - I cleared this one with a mage that swapped on his tank for the second boss. But we couldn't down the second boss while he was on his mage. Basicly, key is to keep the boss at max distance while massnuking. Make sure the energy beings aren't a problem. Boss dies fast otherwise.

Auchenai Crypts - nearly freaking impossible if you ask me, not worth the effort anyhow. :P the first boss is WELL annoying. Positioning needs to be perfect. You prolly need quite a few tries on that. Trash is annoying too. Overall it's a bothersome instance, no fun doing it either. I tried a few wipes on the first boss, got close to downing him, with a warrior tank. But it was getting late, we called it and I haven't gone back since. :P