As this is being discussed, it occurs to me that I'm pretty sure that it would be possible to do a redirect based on referer so that any request to a site coming from an external source (rather than from another page on the site) would automatically redirect to the warning page. You could probably be uberclever and then direct them to the specific page they were requesting after they hit the warning page.

I wouldn't have a problem with doing that for our membership sites or for our 18weststudios.com site, but I suspect that it could be against Google's rules in that it would probably be seen as cloaking or otherwise prohibited.

Anyone know if this would work, and/or what Google's take on it would be?