I came across a blog post by Denise (of the SFC) asking what people consider when determining the difference between a "professional" writer and just an amateur or hobby writer. I hear this question a lot, especially from people who try to say you can't determine what makes a "professional" writer, because it's entirely subjective. As far as I'm concerned, if you say something like that is too subjective, it's not that you can't look at it objectively but rather that you're probably just to lazy to put the thought into it. There are definitely common misconceptions of what makes someone a "professional" writer, and some very basic things that professional writers have in common.
Update: Please note that after further experience with this network and others, my feelings on the subject have changed. I strongly recommend against signing up with any content network (also now known as “content mills”). There are far better ways to kick off your career. You can browse our blog for more up to date information on content mills and better options for your freelance writing career, or