I spent a big part of the summer working on a large scale Flash project through the University of Illinois at Chicago. A major part of the project was section 508 compliance. This presented some interesting problems considering the flash movie loaded in all kinds of XML and images and was fairly dynamic.
Flash 8 has some fairly straight forward accessibility options, but for a project this big and complicated, they really don't help much. This forced me to do a great deal of reading and research.
Now, I've never been a big fan of Adobe/Macromedia's flash documentation. It's (very) slow loading and often contains incomplete and incorrect info. Luckily, they have a comments section for questions, code snippets, and corrections. They also have a blog completely devoted to accessibility. It's not updated very often, but I found some of the material extremely useful.
All that said, I still had to work very hard to get my project to be read by screenreaders consistently and feel like throwing my findings into a white paper could be very helpful to others working on similar projects.
So that's what I'm going to do. Of course, I'll be posting it here when it's finished. Look for it.