I built a reasonably similar ranking system a few years ago, but also taking social media interaction (blog links, delicious bookmarks, etc) with the content items being ranked into account: http://bergie.iki.fi/blog/calculating_news_item_relevance/

You can see it in action on maemo.org: http://maemo.org/news/

PHP sources: http://trac.midgard-project.org/browser/branches/ragnaroek/m...