Great interview with a New Yorker copy editor. Mary Norris, the woman profiled, also has a blog here. The money question and answer:
Andy: What qualities make a person a good candidate for copy editing?
Mary: Self-doubt. It’s always good, before changing something, to stop and wonder if this is a mistake or if the writer did this for a reason. When you’ve read a piece five or more times, it is tempting to believe that it must be perfect, but you have to stay alert for anything you might have missed. Eternal vigilance! It also helps to have read widely (and well), and to have noticed, while you’re at it, how words are spelled. Of course you have to be attentive to details—you have to be a bit of a nitpicker yet be constructive in your nit-picking. You have to love language. And not be too proud to run spell-check.