Someone posted this link to a blog by a writer, in this case, Lynn Viehl. She wrote Twilight Fall, a vampire novel that made it onto the New York Times Bestseller list. It debuted at #19, despite as the author mentions, not doing the things she was told were required.
About $26k from this statement, but after a $50k advance, the actual payment was $0.
So earnings for the year for a best selling author, $50k, of which Uncle Sam and an agent took a good portion. Not a great year, and not what I'd want, or could live on for now. It would be a nice second job, but not necessarily one to support the family.
Granted earnings lag the sales, so perhaps she will get a nice payment on her next statement (slated for Oct 2009).