This article covers part of blogging rhetoric. Rhetoric is the study of how to communicate effectively and persuasively in writing or speech [web definitions].
Organization is an important component in most rubrics for assessing student writing. A specific length is usually part of the writing assignment specifications.
Here are the seven basic blog posting formats:
1. Link-only (few words, a bookmark like del-icio-us)
2. Link blurb (2 lines-few paragraphs, maybe an extract)
3. Brief remark (1-3 short paragraphs)
5. Short article (under 500-700 words)
6. Long article (700+ words)
7. Series postings (500-1000 words each)
"Some formats work best for commentary or explanation, others for alerts and references, etc."
The "brief remark" is "a blog posting that generally is just 1-3 short paragraphs long. It can contain virtually any kind of content: an observation on current events, an idea, an event announcement, a question for readers, an anecdote, a joke, a description, etc."
Of course, Jakob Nielsen must be ranked as number one web rhetorician.