It's a common meme that people often embark on and develop business projects while in graduate school. However, it's unclear how frequently this actually happens in "real life".
More importantly, how responsible/ethical a choice is it, in say, a funded PhD program? I know that typically there is a guideline for hours worked for such a position, but that's almost a joke in comparison to implicit requirements like standards of research quality and publication rate.
Assume that you are a student earnestly engaged in both the PhD topic and an unrelated side project, and you want both the PhD and the business to succeed (i.e., graduate, publish, launch side project as successful startup). To me it seems like the worst-case scenario in that situation would be running into a tough problem in research, while still putting in occasional hours on the side project, as that would look terrible.
I'd also like to hear about the details. How/when to disclose? How to maintain rapport with advisor? What are the ethical concerns? Is this feasible? How do these goofballs in the success stories get away with this? ;)