Flex and Flash might be the way to go for delivering content that can't be stolen from your site. Essentially all content would be accessed from a content viewer built in Flex/Flash. The content viewer would interact with scripts on the back end that serve media files to authenticated requests on the front end. And you wouldn't have to worry about flash extraction tools because they would only be able to steal your content viewer and not your content. This solution isn't 100% hack proof, but what solution is? I would guess it could deter most all content theft.

I see two potential drawbacks to this solution. 1) You require all clients to have Flash installed. With a 98% penetration rate, I wouldn't worry about those 2% who haven't moved into the 21st century. 2) There is quite an overhead proxying all media requests through dynamic scripts like php or ruby that are typically handled by the web server. However, this problem can easily be solved with server optimization and tuning, load balancing, opcode caching, horizontal scaling, etc.

I think delivering content this way would also be better for the overall end user experience with the use of rich graphics, transition effects and behaviors, etc. I'm sure somebody's doing this already???