The WordPress plugin directory has introduced the Change Log tab for plugins that have the meta information provided in the readme.txt file.

Inclusion of the change log is fairly simple as shown in the snippet below (taken from the WordPress Blog):

== Changelog ==

= 1.0 =
* A change since the previous version.
* Another change.

= 0.5 =
* List versions from most recent at top to oldest at bottom.

The WordPress folk believe this will enable the users of the plugins to decide whether or not they want to upgrade, based on the changes made in the new version. This is a concern, especially since the newer versions of some plugins use the WordPress 2.8-specific widget API so the upgrade leaves blog owners who run an older version of WordPress with a broken (incompatible) plugin.