I have a friend who's making enough from her self-published young adult fantasy novels that she quit her job as a .Net/Oracle developer. But most of her writer friends don't do near as well.
She says "tell him you have to sell a LOT to be a bestseller. And if you're an indie, you need someone at the NY Times to like you or you'll never make the list no matter how many you sell."
I'm a long ways from the days when I got into programming because I thought I wanted to be a gamedev but I'm buying Game Programming Patterns just based on how impressed your current book is right now. I'm about to start writing myself and was planning to use Sphinx. Not sure if you're actually using Sphinx for your site, but your design is exactly what I would want for mine.
I agree completely if we're talking about self-publishing technical books. For fiction, my impression is that it's a whole other ballgame.
But, yes, I've been completely blown away too by how well my self-published book did. It really was a life changing experience.