Sam Longoria has a nice essay titled, "What is a Pro?" It's written for indy filmmakers, but I think it applies just as equally to still photographers. To quote: "While skill and/or talent certainly are important, the defining quality of a Professional is payment. Think 'paycheck.' May you earn many big ones."
Amen.
I think this applies equally for grad students and new faculty, which is why I link this into the "Careers" section of my blog. You need to be a professional in how you approach graduate school as well as the job market. Many grad students treat their programs as extensions of their undergraduate years, you need to constantly remind yourself that this is professional training and an extended apprenticeship, and adjust attitudes accordingly.
Good article, mostly agree.
I would just like to add what a pro is not: an ultimate authority of anything related to photography. Unless you also believe a taxi driver is the highest authority on automobiles.
Dirk - I agree. And there are many different types of pros and different type of pro equipment. A Porsche won't always be the best tool, neither will a Humvee (or Ford Caprice), to keep with the auto metaphor.