With the addition of tags to XenForo 1.5 there is a brand new tab in the advanced search page. I don't know about you but it looks a bit cluttered to me. At this point i'm not sure if I should just search everything or if I would have more luck searching for a specific content type. My suggestion is to tweak the interface to reduce the amount of tabs. Perhaps a dropdown with available content types or even better to move the tabs to the search result pages like Google does. From that point on XenForo would know the search term the user is looking for and it may suggest content types based on that search term.