Posting size and frequency should be proportionate to purpose and popularity.
Focused bloggers can afford to post frequently. That discipline yields readership. Examples: Feminist Law Professors, Engadget, ICANHASCHEEZBURGER.
Note that post lengths are inversely proportionate to post frequency: either posts are lengthy and occasional, or short and plentiful.
Also note that you need not read every word to get the point.
Activity of the day: Calculate your Blog Post Proportion (BPP).
Divide your Average Post Length by your Average Post Frequency. This gives you the number of words you expect your readers to read within a certain time period.
What's an appropriate BPP? Well, let's consider Scoble:
It would take the average American, reading at 250-300 words per minute, ten minutes to merely sift through today's 2,300 words of content across 8 different posts... save nothing for the 30 hyperlinks embedded in each post.
Is Robert Scoble worth 10 (or more) minutes of your day? Every day?
Yet, your turd of a blog most likely contains as high, if not higher, BPP. Can you hold a reader's attention for 10 minutes a day, every day?
No. Neither can Scoble.
By comparison: this post, at 207 words, takes the average American less than a minute to read.