After working on, writing for, editing, developing, and connecting Adventure Paths for pretty much the last five years or so, I suspect that I'm one of the ones who knows the most about what works and what doesn't work for Adventure Paths. They're really, REALLY complicated to create, and even now, going into the seventh one I've helped create, I'm still learning how to do it.
But one of the first things I learned was how important those campaign summaries are.
They're vital. They not only let the GM feel like he or she is an organic and valuable part of the thing (which they are!), but they also serve the same role that a movie trailer does; they get folk excited about the coming campaign. If they don't get folk excited and drive them off... that's a failure of the Adventure Path itself, NOT a failure of the campaign overview.
As for how to get them out there for GMs to check out... that's a little more complicated. Do you put them in the first volume of the AP? Do you preview them in the volume just before? Do you put them online? Do you do all three? Will readers get angry that you're "robbing potential content" from a volume because 2 or 4 pages are "wasted?" All important questions.
This thread's actually VERY educational to me, and the main thing I'm taking away from it is confirmation that AP outlines are indispensable to an Adventure Path, and that the best place to print them is alongside the first installment of the first adventure. We did this with "Rise of the Runelords," but in a weird format. With "Second Darkness," I think we've finally hit on the best way to do them; a two-page outline that appears at the back of the product alongside the first adventure. I suspect it's probably also not a bad idea to throw the thing up online somewhere too, so that prospective GMs can check out the upcoming AP without having to shell out 20 bucks or whatever for the outline. That said, chat rooms and mesageboards and blogs and product briefs are also all great ways to get the information out there—we use all four of them for Pathfinder, and despite the fact that we've revealed major spoilers in so doing, sales of Adventure Path products have only increased.
Don't keep secrets from the GM is the moral of the story, I guess!![]()
This post here! I think James hits the nail on the head here, and this is coming from a man, as he says, with experience writing these. Hopefully someone from WoTC takes note

For what its worth, I really like how Paizo decided to toss the overview in the back of the first module of the AP. I think that works best. You can flip to it while browsing the product at your FLGS, but you might consider putting the same overview online as you mentioned. That way it could be made available for potential DMs who might be interested. But as you also said, if you make the overview available regardless, through blogs and messages boards it can spread without needing to buy anything. With no overview, there is nothing you can do but wait till its all out, blindly pay for what may turn out to not be anything to your liking, or just not get it all.