Site reviews

Hi, I have added the ability to review the site as a whole, as well as individual products. 

To do this I changed the ownership of reviews from products to 'reviewable' which is a polymorphic reference. To keep it compatible with the existing views, I have had to add some checks to see what kind of object the reviewable is (product or site) using is_a?. I know this is a bit dirty, however I haven't settled on a cleaner way of doing this yet. If anyone has any ideas, let me know, and I can clean the code up.