Here's a nifty artifact showing the creative process for a very well known movie:
Mystery Man links to the transcript of George Lucas, Steven Spielberg and Lawrence Kasdan's story conference for Raiders of the Lost Ark. It's over 120 pages long.
Reading the summary and skimming the transcript, it's clear that these guys aren't slackers in any sense (even if they were the "Movie Brats"). Lucas' overall vision was incredibly well-thought out, and its a testament to these men's talent in how fluidly they generate and consider ideas.
Amazing that this sees the light of day.