Originally Posted by John Jarrold
As long as it's clearly legible the font doesn't matter. And underline or use italic font as you wish, it makes no difference whatsover to a publisher.
Not to differ for the sake of differing, but I'd say that's not entirely true.
In the day of electronic submissions and desktop publishing, it may not matter as
much to a publisher, but I've seen enough people in the publishing industry to whom it matters enough to that I'm convinced a mono-spaced font is (albeit an old one) the standard. Fonts like TNR and Arial vary the number of characters per line. To some of the people (like copy editor Deanna Hoak, and some agents I've read) who work with hard copy, it matters. They claim less eye strain and better page count estimate accuracies with a font like Courier.
As always, follow submission guidelines if spelled out. But as simple as it is to save a submission in a standardized mono-spaced font, why risk running into the one acquiring editor who's pet-peeve is Arial 10 point (because you wanted to save paper)? Just because it's not important to you doesn't mean it won't be important to someone on the other end.