Agent Jennifer Jackson has a great post on how much of your advance you'll actually get for your precious baby of a first novel - and when. It's a sobering look at the realities that reinforces you must love writing in order to put up with the government-bureacracy-like slowness of the publishing world.
Writer John Scalzi has an equally eye-popping breakdown of the fiscal realities for freelance writers. Thanks to Nephele Tempest (god I want her last name) for the links.
Brace yourself if you choose to read Jennifer's post. Kissing that publishing toad yeilds a prince who still lives with his parents and has $10,000 in credit card debt. And her example uses the high end advance you might expect for a first novel, without deducting what you might spend promoting your book all by your lonesome.
Having said that, I'm psychotically undeterred! If you are too, welcome. You're a writer.