We’ve recently made some changes to help improve the communication between plugin authors and plugin users about the changes that are made between versions.
We feel that all software should have a changelog that details, at a high level, what changes have been made in each version so that the user can make an informed decision about when to upgrade and how much testing they should do with their site.
In order to make this an easy and open communication channel we have added support for a Changelog section in the plugins readme.txt file.? This changelog information is then displayed as a separate tab in the plugin directory and also in the back end of your WordPress blog when you view the details on a new version of a plugin.
The new section is formatted as follows:
== Changelog == = 1.0 = * A change since the previous version. * Another change. = 0.5 = * List versions from most recent at top to oldest at bottom.
We would also like to recommend that you also provide meaningful log messages when you commit changes to the subversion repository for your plugin so that people who want to dig further into your changes can see why things are changing (At the moment is seems a large number of plugin authors leave this field blank which isn’t very helpful).
Read more: http://wordpress.org/development/2009/07/improving-your-plugin-changelogs/