I write slowly. My girfriend, (lisakoski.hubpages.com) is a writer by trade so she pumps them out a lot faster. Depends on the person I guess. Many people write way too many, way too fast. We were actually talking last night in the car about that stupid 30 day challenge. We've both seen hubs from this, and almost all of them are forced, short, low quality hubs.
My point - who cares how many...even one a day is too much imo. What matters is how long do you *need* to take to write a quality hub. This is exactly why Lisa goes faster than I...she is simply a better author.