The permalinks structure is now changed to a category based link structure. This means that individual articles are now accessible via “/category/name-of-the-post/” instead of the meaningless post number. This makes an individual post URI more readable, easier to recall and ‘hackable’, i.e. deleting the postname from the URI shows all articles in this category. Additionally, the pages have nice names, too. As everything this comes at a cost, namely longer link names and a complete new structure to pick up by the search engines. (Their indexing algorithms don’t like changes in the structure of a web site.)