Julian and I are now joint maintainers of the Grid format, so I've updated the plugin's database to the latest version for Moodle 2.3 and Moodle 2.4:
M2.3 -> https://moodle.org/plugins/pluginversion.php?id=2529 -> Needs Moodle version 2012062504.01 release 2.3.4+ (Build: 20130118) because of MDL-36095.
M2.4 -> https://moodle.org/plugins/pluginversion.php?id=2528 -> Moodle version 2012120301.02 release 2.4.1+ (Build: 20130118) because of MDL-36095.
The M2.4 version is considered stable and the M2.3 version is 'beta' although is probably 'stable'. It's 'your' feedback that provides confidence to mark releases as 'stable'.