If you write fiction, you need to read this interview with Joe Konrath, a mystery writer: http://www.bankrate.com/brm/news/investing/20050726b1.asp.
He's a relatively new author: two books published, a third at the publisher, and a fourth on the way. All featuring the same character Jacqueline "Jack" Daniels. I'm going to have to check his novels out. The interview made them seem like funny and involving reads.
He is a novelist who knows that promotion is an important part of the game. He spends 20% of his time writing and 80% promoting his books. You don't have to follow his example to be a successful author, but you do have to put some percentage of your time into promotion, whether it's 80% like Joe or 20%.