http://forum.cmsmadesimple.org/index.php/topic,19380.msg95359.html#msg95359

Content Alias is great at keeping a site structure nice and clean without the
need to jump around into different sections of the site. However, since it
basically duplicates the content and add a different name to the url, this is
seem as duplicated content for search engines.

Is there a way to add "nofollow" (either as default or as an option) to all
links that goes to a content aliased page? This will avoid being penalized. The
original content page will not have nofollow so the page will still be
indexed...just not the content aliased pages.