I'll relate my recent experiences with Mord's Disjunction:
1) I used it (as DM) not once but TWICE in the climactic battle of Good & Evil in our Eberron game (about Characte level 15). One character managed to be in the area of effect, and he lost about 8 out of the 30-odd items he had on his person, and all buffs running on him. He was still a very effective character.
2) It was used by our Cleric in a 20th character level Forgotten Realms game, as we were desparate to stop an attacking epic-level lich. It undid all his spells, and the spells he had trapped the Barbarian with, but the Barbarian lost ONE item -- a set of Boots of Speed. He was still needless to say very effective.
One thing that people might be forgetting is that each item requires a save, using the character's save numbers. This means that only in the most unlucky of circumstances will ALL or even MOST of your items will be destroyed. Further, it usually only comes up in games of level 15 and higher; I certainly wouldn't use it lower than that, because to me it WOULD be unfair, just as it would be unfair to have 10th level PCs tackling a 20th level wizard and his preparations. Maybe as a campaign-ending thing, but not as a regular challenge.
In my opinion, by the time it comes into play, saves are high enough to where it doesn't spell the end of everything if one goes off. As DM I would adjust future challenges and wealth by level accordingly if it did, because to me the game is not a formulaic thing, but a dynamic project that I and the players work to tweak all the time.