In django CMS 2.3 we dropped support for Django 1.2. Django 1.3.1 is now the minimum required Django version. Django CMS 2.3 also introduces Django 1.4 support.
Thanks to the work by Andrew Schoen the page tree in the admin now loads lazily, significantly improving the performance of that view for large sites.
Tests can now be run using setup.py test or runtests.py (the latter should be done in a virtualenv with the proper dependencies installed).
Check runtests.py -h for options.
A serious bug where a text plugin with inline plugins would lose all the inline plugins when moved to a different placeholder has been fixed.
The CMS_FLAT_URLS setting is deprecated and will be removed in version 2.4. The moderation feature (CMS_MODERATOR = True) will be deprecated in 2.4 and replaced with a simpler way of handling unpublished changes.