Frostweave Cloth

I have found the Holy Grail of all Frostweave Farming locations.
I read all the comments, some places were good, but I simply don't have the patience to get a few cloth here and there, especially on a PvP server with gankers.
Cathedral of darkness is NOT that great.
Without anymore blabbering...

Step 1:

• Head to Naxxramas on 25 Player difficulty; Save yourself past the 1st boss of the Plague Quarter by defeating the first encounter. Note: If you are not level 85 or higher but wish to farm this, you may need a helper just to defeat the 1st boss one time in a given week and then you can feel safe to continue solo farming.

Step 2 (The fun part):

• The bats after 1st boss can be mass pulled at one time, ALWAYS dropping between 30 and 40 (sometimes 50) Frostweave in ONE pull! This is without the Tailoring bonus for extra cloth! Those with the Tailoring Profession can expect anywhere from the same to far greater results.
  Note: Remember to loot the corpses multiple times, as sometimes so much cloth drops that it does not fit in the 1st loot window thanks to mass looting.

Step 3:

• Afterwords, run out, reset the instance, and then switch the difficulty to 10man (Don't worry, this is a one time difficulty change, and you will stay on 10 man the rest of the week.)
  Now run in, mass pull bats, loot your crazy amounts of cloth, run out, reset instance, repeat!

* Not kidding I got upwards of 10 to 15 stacks in around 10 minutes without the Cloth Scavenging bonus!
* For the seasoned and hardcore farmers, I recommend keeping a stack of Darkwater Potion on you for all your runs to truly get the most cloth for your time spent. (Note: this is completely optional and not required by any means.)
* On a side-note, you can also expect to grab quite a few pieces of random gear, ranging from high vendor greens, to high AH price BoE epics!

- Obviously you'll then have a waiting period since you can't enter more than 5 times in an hour, but oh lord is it AMAZING! Forget these places people are saying has high drop-rates, this is quick, painless, in/out, immune to PvP gankers, and anyone level 85 and up can do this, which I'd assume you would be if u expected to farm Northrend mobs fast in the first place.
- As you're waiting for 5-Instance/hr limit to reset, you can be using your cloth for leveling that pesky Tailoring, making bank on the Auction House, or slow-farming some of the suggested places from other users in your down time, and as soon as the hour is done, hit up Naxx again for more loads of cloth, as often as you like all week!

Please try this out, and Up-Vote if it helped!

EDIT: Created an easier to follow step-by-step. Do not worry, both steps 1 and 2 are to set up your cloth farming for the entire week. After you have done the 1st two steps, you can enjoy an entire week of running in and out of Naxx collecting you cloth by the truckload without any additional steps.

EDIT: As posted below in a comment that was down voted (don't know why)
You do NOT have to continuously switch between 25/10. The reason for this is very often (as some have seen) simply running out and resetting the instance without changing difficulty sometimes does not reset mobs if you are saved to that raid. By starting on 25 just 1 time in a given week, then switching to 10man and resetting, it seems to avoid the mob reset bug that some of you have experienced. After the first switch, feel free to stay on 10man for the rest of the week.

Finally: A BIG THANK YOU to all you Wowhead users for getting this post to the #1 spot! Even though I've just discovered this late into patch 5.2, it's great to see the community is always out there looking to improve the gaming experience for others!

Just a quick FYI for all First Aiders out there: Once you set foot in northrend and this Frostweave cloth starts to drop, you can make:

-"Frostweave Bandage": Heals 4760 damage over 8 sec; Requires 350 First Aid to use.
Then you will be able to make:

-"Heavy Frostweave Bandage": Heals 5480 damage over 8 sec; Requires 400 First Aid to use.

PS: Rate up if this was usefull in any way whatsoever.

EDIT: As the reply to this post states, dense and purified frostweave bandage were removed before live.

What I found by far most lucrative and cloth-yelding was the Onslaught Harbour (The islands west of Icecrown), with most mobs dropping 2-4 cloth. I'm an 85 boomkin in restogear, and for those of you not above 80, this spot might not be so good, due to the risk of massive pulls.

My tactic was to first pull the mobs on the staircase of the monastery and then run in the entrance and using LoS getting them all in a neat bunch, then you just take whatever AoE you have available (Wild Mushrooms in my case) and blast away. Then I went in further into the church and pulled the two big groups in there, (same procedure, LoS + AoE).

After having emptied the monastery I went to the westernmost part of the northern island where the mobs are a bit more spread out. There i just DoT:ed and ran, killing all of them and then looting. When this island was empty I went towards the cave on the southern end of the island, where there are three large groups just outside. I aggroed all three and and used LoS again, this time using the cavern walls, and then blasted them down.

When I had done these three places the ones in front of the monastery had respawned, so basically I just went in a circle between these three spots and that yielded me 15 stacks of Frostweave and a gazzillion of greens in less than an hour. Hope this helps :)