This "RSA Animate" provides some insight into what drives software engineers to create software such as Linux, and give it away for free. This seems to imply that giving back is a reward in itself, but in the back of the developer's mind there could also be the idea that he may become famous some day, and that the money will follow. As a systems administrator / developer, I tend to agree with the idea that becoming an expert does not always require any compensation, and it feels good to help fellow sysadmins and computer users. The knowledge itself is valuable, and can be turned into a business at some point. For example practicing a musical instrument, or learning to cook well for no monetary reward can be fun, but is also something to fall back on. RSA Animate - Drive: The surprising truth about what motivates us This lively RSA Animate, adapted from Dan Pink's talk at the RSA, illustrates the hidden truths behind what really motivates us at...
They say the only sure things in life are death and taxes.