One of my favorite instances, ran it through 8times in one day in search of illusionary rod, triune amulate, and whitemane's chapeu...

this instance has some of the best drops...thats the main reason why people do it...
Also, there is  glitch in there(for mages:

Steps:
Go in Library Instance
Face the Exit, but be against the wall
Run towards the instance(as if exiting)
RIGHT before you touch the cloud looking thingy of the instance, use blink

If you do it right, you will blink right past the exit and be in a room

This room will be the room were you pick the instance to go in, but all the instances are blocked by walls

Youll see a grey wall...walk into it and jump...there are 2 guards you can kill

The room is very cool...it has clouds, and the sun in the distance..but its a grey floor, REALLY big...

If you get to the edge...you can try to jump, and you stay floating, then just blink out...(you dont die)

But be careful of holes in the floor, if you fall, you die...even if you use slowfall...

Theres one with a chest in the middle...dont get it...(you die)...

Anyways, try exploring it...its cool, you can see floating skeletons/guards/dogs sometimes....(and you can mount also)

^_^ Enjoy