Jay Goltz posed this question and receive definitions all over the place on the New York Times You're the Boss Blog.
This is a subject that is repeatedly coming up in Academia and in Business. Frankly no one really has definition of Social Entrepreneurship that most people can agree upon.
Rutgers University, several months ago, ran a symposium just on this subject. The purpose of the conference was to develop a definition for a Social Entrepreneur and prepare guidelines for a Social Entrepreneurial venture. There were no conclusions.
However Social Entrepreneurship will repeatedly be in the news so keep you eyes open...