Infrastructure changes, code cleanup, bug fixes, … The permalink generation code has changed quite a bit and now supports %author% and %category% and paging everywhere. Most of the logic in wp-blog-header moved into query_posts(). There are some new functions for determing what type of page is being displayed: is_single(), is_archive(), is_category(), is_home(), etc. Several new plugin hooks have been added. Lots of work went into fixing the backslash problems and removing unneeded calls to stripslashes(). index.php can now serve up feeds and trackbacks. Just slap &feed=rss2 onto any index.php query to get an rss2 feed of the query results. posts_nav_link() now uses cruft-free URLs. /page/# can be appended to any permalink. /feed/ can be used in more places. PATH_INFO can be used to handle all permalinks, including feed and trackback. And lots more.