I created a number of tasks and subtasks, but KOrganizer ignored the tree and sent all the new sub-tasks as top level tasks. This didn't affected only the sub-tasks created through KOrganizer though, the sub-tasks created through the google calendar/tasks webapp remained in their position. I'm using KDE 4.8.0, akonadi-google from git master, and tried both SQLite and MySQL backends for akonadi
According to http://www.progdan.cz/2011/09/akonadi-google-resource-tasks-support/ the bug is already known
Thanks for taking time to report the problem. This issue has been fully fixed for libkgoogle 0.3 (see bug #285040). I have committed part of the patch to master now, so that the hierarchy is preserved for newly created items. Moving sub-tasks between parent tasks or converting top-level tasks to sub-tasks does not work though, you have to wait for 0.3 :)
For reference, the commit is master/8caa43f54df5f4593df65a906607b888982d3599