Don't get me started on this.
Thorim has managed to turn into our guilds current cock block.
Thorim currently has issues with lag and DCing, and if it coincides with Wintergrasp we have zero chance of doing anythign useful on this boss. Anyone with a slightly dodgey connection, Thorim will eat your connection and spit it out covered in goo. As you run in, it is guaranteed 1-25 people will DC. No jokes. Just hold off DPSing down the initial "entertainment" before engaging the boss until all the DCers are back online. We do a ready check before starting the event.
Thorim has a lot of aoe, and many many many adds. Do everything in your power to minimise CPU/GPU/bandwidth issues on your PC. Turn graphics down, turn OFF as many mods as you possibly can, stop FRAPSing, face walls etc etc. This place is WORSE than Dalaran.
Anyway, assuming you get past the DCs, there are a few tricks you NEED to do.
Arena: 2 tanks - one for champions, one for evokers. Evokers heal, so they need to be interrupted and killed asap. Champions are just plain nasty and need taking out. You can and should Disarm them to prevent WW, get your rogues, surv hunters and DPS warriors onto it. Your DPS MUST assist the 2 tanks when they call for DPS. Apart from that, AoE mobs and do your best to stay alive. All your healers should be raid healing in there, the splash damage is NUTS!
Gauntlet: If your team know what they are doing, I solo healed this (with an OH throwing up some Hots occasionally) as a Holy Pally. So very doable. Its preferable to have at least 1 CC (hunters, shammies, mages) 2 if you only have 1 tank. Engage mini boss as soon as possible. With the second mini boss, have an OT pick up the adds and get a hunter up the stairs and MDing the next miniboss to the other tank ASAP. And I mean, as soon as the doors open. Burn the mini boss down at the bottom of the stairs for more room for running away from people with the bomb. Then run up the stairs (ignore the adds completely). DO NOT run into the big circles or big purple bubbles will make life unpleasant (run left or right of them).
Then engage thorim.
Run away from the lightning on the floor (the further away from thorim you are the further away you have to run from the lightning) and BURN LIKE CRAZY!
That's about it. Enjoy!