Have you been asked to work for free in exchange for "exposure" or promises of paid future work?
This article is a good read for anybody who is freelancing or running their own business. Although it involves a designer, this same sort of solicitation often crops up with coders and other technical professionals.
... it's not just designers. I received a ton of responses from writers, cartoonists, architects and people in other professions who get asked to work for free. I don't know what it is. Maybe people think that if you went to art school you don't understand money?