So, as Matticus says, "Use them. Please." It makes a lot more sense to use the cooldowns on a regular basis (like, roughly every time the cooldown is up) than it does to hardly use them at all, or only in situations where it's too late. Now, if you're like me and you think about this for a while, and reluctantly agree that yes it does make sense, then you come up with another problem that you want to use these cooldowns only at moments when it'll be most effective. On my hunter, for example, I hate to use "Bestial Wrath" (and "Beast Within") unless I believe there's at least 18 seconds left in the fight, because I hate seeing myself and my pet all Big and Red with nothing to kill!
But the plain and simple fact is, people like me need to be less stingy with cooldowns. I don't mean we should blow them at moments that don't matter, of course, rather we would do better if we used them much more often, especially when they're not absolutely necessary to succeed. They can help the various sorts of grinding, farming, and trash-mob fighting go by a bit faster, and sometimes in long boss fights you can use them more than once!
Can you think of any cooldowns that you think should be saved for that somewhat rare panic-button moment (such as a rogue's "Vanish," perhaps)? Can you think of cooldowns that you see people often forgetting or hesitating to use?