I'd like to comment on the 'workload required for AP' topic in here. So I'm running PotA right now, and I'm finding that I do basically no reading or other preparation before each session. I mean, they decide to go into the next part of the dungeon, and I spend five minutes before the game glancing over those rooms and noting which monsters are there; or they decide to visit Womford, and I glance over those pages and start speaking. But the flipside of this is that I carefully read the book twice before running it. I first read it cover to cover, like a kinda boring novel, and then I skimmed through it while writing down every named NPC and the pages on which they appeared. I revised it, in academic terms.

I focused on the NPCs on the theory that the biggest problem I would face is players asking, "What was that guy's name? Where did we meet him?".
My observation is that successfully running an AP does involve a fair amount of time on the DM's part, but that that time is mostly front-loaded. I am running the book exactly as written, so that affects my experience, but it is clear that the time and effort spent is mostly located prior to the campaign's start. This is in contrast to my homebrew game, where not only did I have to do world building before the game started, taking easily as long as reading the PotA book, but I also have to spend time every week thinking up plots, trying to decide how to direct the players forward, and deciding upon an outcome for each story element in play. There is more work to be done in my (low plot, but not quite sandbox) campaign than there is for the Adventure Path. The latter has the considerable benefit that I have basically completed all of the work that I need to do for it, and I can now coast through the rest of the campaign upon my memory and understanding of the book's contents.
I found the same for Ravenloft I6, it is worth noting. That would be a friggin' nightmare to run without reading it cover to cover first - you really need to understand the castle's layout as the DM, since the players certainly won't.