Being a confessed alt-aholic, I will occasionally find myself running on an alt I haven't played recently and a bit confused about my hotkey layout. Why doesn't hitting "2" cast Power Word: Shield? Oh, wait, I'm playing my rogue... After playing one class for a while, it's easy to get accustomed to pressing the right buttons by habit, and while I try to arrange my buttons in a way that similar situations (across different classes) will use similar hotkeys this (obviously!) doesn't always work. So what's the one skill you have trouble living without when playing another character? For me, it's usually priest's ubiquitous heals -- even though they tend to be counterbalanced by the greater damage abilities.