The Joomla! open source WCM community today released version 1.7, just 6 months after the release of 1.6. Perhaps because the development team has been busy stabilizing a 1.6 trunk that was packed with many new features, version 1.7 does not offer much of significance for end users.
Our Web CMS evaluation research will outline the impacts of all this in more detail, but the biggest news for now is that version 1.7 represents the first to formally segregate a base layer -- the former "framework" now known as Joomla! Platform -- from the higher-level Content Management System (CMS) layer.
This separation of "framework" and "CMS" has become almost universal in the open source world, but the transition is fraught with complexity for licensees. On the plus side, you have the freedom to develop custom applications off the Joomla! Platform, leveraging core services like security, database handling, logging, without having to use or getting tied down by the restriction of CMS layer.
On the down side, it means two different (albeit related) environments for the all-important Joomla! add-ons -- called "extensions" -- to address. This could complicate compatibility going forward.
Note that last year Joomla! adopted release timelines based on a strict schedule, rather than it's-ready-when-it's-done, feature-based releases. Version 1.6 was the first release as part of this plan, now followed by version 1.7. Perhaps more importantly the community now makes a distinction between long-term and short-term releases. These will happen on different time cycles and thus will affect the core platform versus the CMS differently.
Given the large base of extensions (just about 8000), I think the community will be challenged to keep everything in sync. Even today, a sizable proportion of the Joomla! community still remains on version 1.5, since a significant percentage of Joomla! extensions are not supported for version 1.6. You the customer will need to pay even greater attention to compatibility going forward.