I think a good compromise is to create a firm "site map" (essentially a flow chart of all pages and links) so that the architecture of the site is set, but the actual words and pictures can come in a more piecemeal fashion. This way, there is a firm structure to drop the content into.

I know that this isn't a perfect world and this system will inevitably lead to some "oh, now that we are writing this, we think that page should go somewhere else" cases, but at least you have a firm, agreed upon structure. That way, when the client deviates from it, it's more obvious (as nothing is ever truly obvious to a client) who is causing the delays.

my $.02
- monster.