As a copyeditor, I really appreciate writers who use Courier. Times is very dense, and it's harder to spot typos in it. Also, because it doesn't take up as much room, I'm expected to copyedit more words per hour than I am with Courier. (Most production departments--and I say this with fifteen years' experience--expect a freelancer to copyedit ten pages per hour, regardless of how those pages are formatted.) That's a lot when you have as many things to take care of in a manuscript (http://deannahoak.livejournal.com/38288.html) as we do.