Isn’t this another version of the question: “Is it Quantity or Quality that it’s important?”
The answer is within you, and more than an absolute answer is a question of the right mix, the right balance between frequency and relevance. A lot has to do with the intended outcome for the blog, its authenticity and how it fits within the overall meta outcome of your project, congruency still rules.
Once a day seems to be the rule for the majority of A-list Bloggers, voice on the blogosphere has the magic number at at least once or twice a week; in all effectiveness still dealing in terms of Quantity. Lately the discussion is migrating to Quality, and there have been a few interesting posts like Erik Kintz’s , David Chen’s and Seth Godin’s, who make the argument that relevance to your audience is more important than frequency.
So, here’s your answer: be authentic, stay congruent, and blog for quality.