The majority of introduced enhancements concern mostly programmers, who now will be able to create websites quickly and efficiently.
The most important changes are as follows: improvement in session cookie handling, better processing of big XML-RPC payloads, compatibility with PostgreSQL, PHP 5.3, PHP 4, CSS and JS, also improved login for login failures.
Due to a serious security bug, new edition of Joomla has been released.
The most significant fixes introduced in CMS Made Simple 1.7.1 is better support for SSL. Now it's possible to tick which page is to start in HTTPS.
On the 23 April Joomla 1.5.16 was released. It had some serious security bugs. The first was connected with supporting PHP versions earlier than 5.2. The second one concerned Session Hangler parameter set to None in Global Configuration.