Justine Musk has an excellent essay on her career as a novelist in the mass market paperback salt mines and it is very good. It involves numbers and market realities and other concepts that make the writing-is-art! crowd nervous and/or cranky.
Note: I do not think writing-is-art and publishing-is-a-business are mutually exclusive notions. I think that in order to do the one it really behooves you to understand and get your head around the second. Even if in doing so you conclude that you’re better off self-publishing. Or writing your novel in a series of haikus on the back of Anzaac bickies and floating them out to sea at dusk each night for the next ten years.
Have I mentioned that it took me many many years to make my first professional sale? I seriously thought about doing the floating biscuit (cookie) thing. If only I weren’t so bad at writing with icing.