Linking To Mirrors & Penalties?

[Sleep[Walker]]

I think you can be banned by LLs for using robots.txt to disallow SE to crawl freesites. Link list are giving recips not only for direct clicks on your warning page, but also to have inbound links. And if you put your freesite's warning page into robots.txt, all the LLs' links won't come into count. Maybe you're allowed to include gallery pages... i don't know.

Google doesn't penalise for duplicate content

Respectfully disagree. Google penalizes for duplicate content and it is one of the most serious problems nowadays. Even such things as feeds or print view can lower your site on several positions. There are hundreds of articles on this topic, try to use search engines, google's official help and google official blogs.