I recently got a bunch of submissions from a user editing trivia/allusions that involve titles of books that were previously underlined, but the user wants to change it to italics, stating that "according to TV.com's rules underlining is never allowed". I was under the impression that it was proper to underline the titles of books (from all of those lovely years of English grammar classes), and I cannot find anywhere on the site that says that underlining is "never allowed"...

Does anyone know what the real rule is? Should I go ahead and change all book titles to italics or leave them underlined?