Aggro Me: Mad Skillz
On my wizzie, I used to grab every +disruption item I could get my greedy overnuking hands on. Then I would brag about my massive disruption skillage and talk about how it would improve my spell damage and make me an even more awesome wizard than I already was.
Yeah, turns out that made me an even bigger noob than I already was. Disruption skill does not represent what I thought it did. Perhaps everyone who reads this blog might realize that already, but just in case a few don't I thought I would try to explain it (and the other similar skills). This is the best explanation I can come up with from some extensive forums research:
Disruption - A higher disruption skill increases the chance that you will land a disruption spell on a mob. Looked at from another angle, a higher disruption skill means less chance of a resist for a disruption spell.
Ministration - A higher ministration skill decreases the chance of a fizzle for a ministration spell.
Things to note:
A higher disruption skill has no effect on the damage a spell does. It might, however, increase your overall DPS because you land more spells over a certain period. Ministration does not increase the heal amounts on your heal spells, though it might make you a more successful healer by preventing the dreaded fizzles.
There are other factors that figure into spell resists, notably a mob's level in relation to yours and it's own resist numbers.
Negative spells (i.e. damage, debuffs) never fizzle but can be resisted. Beneficial spells (heals or buffs) are never resisted but can fizzle. So the other skills (focus, ordination, subjugation, etc.) fit into one of these two categories. For the skills dealing with negative spells a higher skill will equal a greater chance to land the spell (less resists). For the skills dealing with beneficial spells, a higher skill will equal a greater chance to cast successfully (less fizzles).
Of course, this is just my interpretation of what I read on the official forums and may be inaccurate. Here's one thread but there's a bunch more out there with similar questions.
Who cares? Well, knowing what the skill increases on an item do can help you be a better "consumer." Now, obviously it's never a bad thing to have less fizzles or resists. But if you find yourself never fizzling or being resisted, you might want to go with items that have different beneficial properties. For example, you might give up some disruption skill for more power.
This also serves as an introduction to a post I'm working on about the relative triviality of gear improvement for int-capped max-level mages as opposed to other classes. But I have to think about that one some more so watch for it at a later date.