If you run into a Layered Navigation error in Magento where in your product views there is either a) no filtered navigation or b) doesn’t seem accurate, here is a pretty good fix. I don’t believe that this is a problem after 1.4 but I could be wrong. http://chrismckee.co.uk/magento-commerce-layered-navigation-cache-error-part-badger-part-duck/
Magento Layered Navigation Problems Solved