The Joomla Project announced the immediate availability of Joomla 2.5.0. This is a security release including 26 new features, 4 security issues fixed and 356 tracker issues fixed. Along with new features such as advanced search and automatic notification of Joomla core and extension updates, the Joomla CMS for the first time includes multi-database support with the addition of Microsoft SQL Server. Joomla 2.5.0 is is the next update from version 1.7.
Version 2.5 is a so-called long-term-support (LTS) release that will be supported for at least 18 months by the project. Joomla 2.5 adheres to Joomla’s newly-adopted six-month release cycle that began with the previous Joomla CMS release of Joomla 1.7 in July, 2011. Using the latest version of Joomla is the best way to ensure organizational and personal security needs are being met since it will have the most recent updates to protect against the latest security threats.
Version 1.7 will reach end of life on 24 February 2012. All users of version 1.7 are advised to update to version 2.5.0 before that time.
Because the changes from Joomla 1.5 to Joomla 2.5 are so large and because of the massive effort put into getting Joomla 2.5 to where it is today, there is no core upgrade path, this is indeed a migration.