My understanding of how this spam tactic works is that when a searcher visits a page the second the mouse hovers over the page contents or background, the page redirects to a new page. So the first page (the one that initiates the redirect) contains keyword stuffed content that is not meant for the end user. Search engines rank this page high in the rankings and then when a searcher goes to it, they are automatically redirected.
Now Google is filtering out this type of spam tactic according to jimh009 at WebmasterWorld. GoogleGuy offers some support for those that were tricked into using this spam tactic by an unscrupulous SEO.
Again, make sure you completely remove any doorway pages or links to spam that an SEO convinced you to put on your site before you write to Google about reinclusion. It reflects badly on your site if you write about reinclusion and then we check and the spam pages are still live on your site.
Good move Google - makes for happy searchers.