Given today's average attention span, it seems like five paragraphs is about it. If your goal is to be read, I don't think you have much more opportunity than five paragraphs. Look at today's blogs. I don't think they go on for pages and pages (although to be honest, I haven't seen enough blogs to be able to say). Plus, I think somebody somewhere did research on how people reading in front of screens can't (and don't) read pages and pages of text.
For the average writer, expecting more than five paragraphs is probably both not practical and a bit unrealistic. If you're an average student, I would guess (condescendingly, sorry) that you don't have the attention span to write more than five paragraphs regularly. If you're in the workplace, your bosses and coworkers don't have time to read lots of stuff. And if you're a blogger, well, you have to deal with that attention span problem.