I must respectfully disagree with @ETpro. The publishing world is in a state of flux and also confusion. Self-publishing is no longer stigmatized, Internet publishing has gained respectability, and publishing houses like everybody else are taking a whipping in these economic times. Big houses are eating small houses alive and at the same time small independent presses are springing up. So say my sources. So it’s anybody’s guess.
One author I know who successfully sold her first book is keeping her finished second in a box and not even submitting it right now, while working on her third. She doesn’t even want to send it out into the current maelstrom. Another that I heard of had a book accepted by a publisher who bought the rights and then folded before press time, leaving the unpublished work in limbo.
Common wisdom seems to be that if you can sell 5000 copies of a self-published work and you also have a strong “platform” (and you are eminently presentable for the talk show and PBS radio circuit and the infinite cycle of bookstore signings and conference appearances), you can get a commercial publisher to take an interest in your work.
The big down side that I see is that no author is capable of judging the print-readiness of his or her work. Commercial publishers put a book through a vetting process and don’t take it straight from raw ms. to press run. I have seen quantities of self-published work that had great promise but desperately needed the attentions of a competent editor. Unless you plan to pay for a real edit by a real editor, even before you get to the cost of printing, the labor of distribution, and the ceaseless effort of promotion, you might as well just pay a few dollars for a domain name and web hosting and upload it to your own website to share with your friends and make your mother proud.