Written by:
Mihai Moscovici
11:23 Usability improvements: vertical tabs, permission screen, new defauld fronpage, default minimal profile.
11:25 Improved UX.
11:28 Toolbar: new IA along the top, shortcut bar for role-specific frequent access.
11:29 New admin theme called "Seven": overlays, edit in place.
11:30 Changes for site builders: new minim system requirements, timezone and country support, users can cancel own accounts, mix&mach public and private profiles, internationalization, native image handling (needs your help).
11:34 Security: e-mail notifications, php filter module, Cron.php requires key in URL to be run, new permission for running site updates, limit login attempts for better flood control, stronger password algorithms.
11:36 CCK: new fields type in core. Fields be applied to nodes, users, comments, taxonomy terms.
11:38 Many pages elements are now blocks/regions.
11:39 Re-vamped* .tpl.php: re-engineered XHTML, standart, semantic.
11:41 $contenmt is now an array of page properties that keeps track of what's been printed so far.
11:42 Javascript improvements: jQuery 1.3...
11:52 Faster, more scalable Drupal: proxy, XDebug, innoDB, CDN support for files
11:53 No more $op
11:54 New $page object
11:55 Lots of API: roles, filter, caching, locking framework
11:56 Node access improvement
11:57 New install profile
Get the full list of changes Drupal 7
CHANGELOG.txt
http://drupal.org/update/modules/6/7
http://drupal.org/update/theme/6/7
http://drupal.org/project/coder