I was going to split this up, post some today and the rest later, but I decided this was better. On Stephen Watkins' blog we've been talking about exactly what a "scene" is, and when you post serially a "scene" is pretty much one post, one day's excerpt.
A couple of times I've been on blogs where people have talked about where to break chapters, should it be a cliffhanger, and I never really have much to contribute. I have no theories about this; it's pretty much always a gut decision. I sometimes write something and think, "This would be a good curtain line," but then it doesn't end up working that way.
In one of the Nero Wolfe mysteries (called Plot It Yourself), Wolfe is investigating a series of plagiarism cases. In each cases, it's different person bringing the charge (against a different writer), but Wolfe gets the idea that the cases may be related, and compares the manuscripts on which the claims are based. He discovers they were all written by the same person.
He identifies similarities of punctuation, sentence construction, and specific words. Then he says:
A clever man might successfully disguise every element of his style but one – the paragraphing. Diction and syntax may be determined and controlled by rational processes in full consciousness, but paragraphing – the decision whether to take short hops or long ones, whether to hop in the middle of a thought or action or finish it first – that comes from instinct, from the depths of personality. I will concede the possibility that the verbal similarities, and even the punctuation, could be coincidence, though it is highly improbable; but not the paragraphing. These three stories were paragraphed by the same person.
That's how I feel about deciding where to break excerpts in serial publication.