Some of my writer friends over at the Chiseled in Rock blog today have An Interview with Chuck Sambuchino, famous for his Guide to Literary Agents Editor's Blog.
Among many other things, Sambuchino says As writers, we all have certain hopes for our books. We want them to be in every bookstore across America. We want them to be translated and available in Europe. We want a book tour. Essentially, we want the book to have a chance to break out and sell lots of copies. Etc., etc. To do these big things, you need to get published by a large publisher who can make these goals realities. But big publishers won’t take unsolicited submissions from writers; you need an agent to get the attention of the large houses in NYC and elsewhere.
He has a lot of other good info. Check it out.