Drupal 6.20, a maintenance release fixing issues reported through the bug tracking system, is now available for download. There are no security fixes in this release. Upgrading your existing Drupal 6 sites is recommended.
Highlights of changes in this release include settings form inheritance for subthemes, syslog identity configuration support, better update support from Drupal 5, support for the tel: protocol, several fixes to the node translation system, fixes for CSS aggregation with non UTF-8 characters, support for specifying database collation, more complete coverage of HTML entities in entity decoding and various documentation fixes and other smaller bugfixes. In total almost 50 patches were committed to improve Drupal 6. For more information about the Drupal 6.x release series, consult the Drupal 6.0 release announcement
The full list of changes between the 6.19 and 6.20 releases can be found by reading the 6.20 release notes. A complete list of all bug fixes in the stable DRUPAL-6 branch can be found at http://drupal.org/project/cvs/3060/?branch=DRUPAL-6.
The robots.txt file was changed in this release to allow for uploaded files in /sites/ to be indexed by search engines. See http://drupal.org/node/494462 for more information.
The default.settings.php file also introduced another commented out setting to accommodate for the new database collation support. Unless you'd like to specify that setting, there is no need to modify your settings.php. Moving to a different collation on existing databases requires converting data! It is suggested you read the whole commentary in default.settings.php and on the issue (http://drupal.org/node/772678) if you'd like to use this possibility.
The release did not change the .htaccess file however, so you can keep your existing file intact, if you have modifications in it.