I sold more than 4,000 books (closer to about 15,000), but have basically made a relatively comparable amount of money from royalties from the book.
That said, if you're writing a book looking to profit from the sales of the book, you're doing it wrong. I easily pull in six figures for speaking fees that result from having written a book. I wasn't getting those offers before having written the book.
Maybe fiction is a bit different. But you can always find a way.
1. Hacking: The Next Generation (Animal Guide) - http://www.amazon.com/Hacking-Next-Generation-Animal-Guide/d...
2. Discrete Mathematics for Computer Scientists - http://www.amazon.com/Discrete-Mathematics-Computer-Science-...
3. Imagine: How Creativity Works - http://www.amazon.com/Imagine-Creativity-Works-Jonah-Lehrer/...
4. The Information Diet: A Case for Conscious Consumption -http://www.amazon.com/Information-Diet-Case-Conscious-Consum...
http://www.amazon.com/Information-Diet-Case-Conscious-Consum...