Authors who have already been published and sold hundreds of thousands of books can get away with things that you and I, Green, had better not contemplate just yet.
Even a humble individual like myself, submitting to an editor who has already published one of my books, has a bit more leeway than someone trying to make a good first impression on an agent or editor who has never heard his or her name before.
And what you submit and what eventually gets published are two different things as well. If an agent asks for three sample chapters, I think it's a safe bet they aren't looking for 30,000 words.
Paradox, not everyone asking for a synopsis wants the same length. Most agents either ask for one page or three pages -- but then there are the mavericks like my agent who asks for two. Most agents want double-spaced, but some who ask for only one page want single-spaced, with blank lines between the paragraphs. Find out what the individual or the agency wants before you submit to them -- you'll probably need every single word they'll allow.
Brian probably has some great links under the Resources heading. But keep in mind that often an online sample synopsis is NOT the synopsis for that writer's first book. So what I said to Green up above may apply.
But here is the thing, and after that I'm going to shut up: No reasonable agent or editor is going to reject your proposal because of one little thing that you do. (Of course they all have different ideas about what constitutes a tiny mistake and what they regard as a damning sign of unprofessionalism.) They WILL reject a manuscript or a proposal for a series of small things, particularly if those come before they get a chance to read the best parts of what you've submitted.
Some of these things you can't predict in advance. They may hate the title of your book because it's too cliche (or not cliche enough). Yours may be the fourth book with a similar premise they've looked at that week, and all the others were horrible, so that their first response is, "Oh my god, here we go again." The edition of Writers Market that you consulted may have garbled their name, so you've naturally repeated that mistake in your cover letter. (This actually happened to me, and while I don't say that this was the only reason the ms. came back with a form rejection, it could hardly have counted in my favor.)
If you start out with one or two strikes against you that could have been avoided, these may add up, along with the things that you can't predict, to an early rejection. If you think that the way you have your chapters divided up is so important that it's worth taking that risk, it's up to you. You may even be right. But wouldn't it be a pity if they stopped reading a page too soon -- just before they reached that killer scene that would have inevitably sold the book -- only because you decided to be inflexible where it wouldn't have really hurt the story to make some adjustments?
These are the things that each writer has to weigh and consider, and decide for him or herself. It's just better to know what may be at stake before you start that process.