I've noticed people have a specific 'pattern' to how they layout skills in they're bar. For me, I start with offensive and work my way to defensive from left to right.
Sometimes I'll swap out an offensive, for defensive spell and head out on a quest or a guild member will enter the mission. As I'm going along I instinctively click on my defensive spell because its the 2nd one in the skill list moving left to right. Causing me to cast the wrong spell over and over. "OOps, I forgot to re-order my skills before we left town, can we go back for a second...?"
A few guild members have done this a few times with they're fighters too (casting "I'll avenge you!" rather then they're bleeding spells). But once your out in battle you can't alter the order.
It would be great if you could

CodeMonkey