The title is one of the ways your eye is drawn to a book - along with the cover art, (and of course, don't forget the author's name) with the intent of getting you to pick up the book and see what it's about (by reading at least the blurb, or preferably, the whole book). So, a unique title at least will be a great help in that goal.
Michael A. Stackpole of the same title, which is set in a very interesting and unique world. I've read and enjoyed both books a few times now (and writing this out is making me want to re-read the Michael A. Stackpole book). But they're not alone. Amazon.com comes up with about 80 results with the search term "Once A Hero".
Sometimes even books with similar titles can get confusing too: for example Elizabeth Moon's Paksenarrion books: Oath of Gold (the third book in the Deed of Paksenarrion) and Oath of Fealty, the most recent book she's published. Every now and then, I get the two confused in my head for a minute. Or the Blood series by Tanya Huff. Except for the last book, Blood Debt, I have no clue as to the reading order without actually looking at any of the books, nor can I remember which events are tied to which books.
Most of the time it doesn't bother me, because I know which book I'm referring to, but now and again, it gets confusing when I'm talking to others. What's your take on books with shared titles?