Some positive aspects to writing articles and selling them on the internet is that you get to supplement your monthly income. In this rough economy who can't use a few extra bucks? Another upside is that you can build up your cache of original content and increase your reputation for writing and possibly attract some higher paying customers. Lastly, just think of the knowledge you are gaining by having to research some of the topics you write about. You are, or will soon be, a fountain of useless information.
The most useful thing to do is always to locate a listing that perhaps not only pays you for your original post but one that additionally provides continuing residuals for every period your article gets read. The recurring might not be world-shattering but if you've got a group of articles that regularly get read afterward your fee may be worth the difficulty.