What you must know

  1. Only the common subset of task properties are synchronized
  2. Deletion are synchronized. If you delete a task at Google, it will also be deleted in Outlook permanently and vice versa.
  3. Make sure your system clock is as accurate as possible.
In detail:

1: Google Tasks have in general fewer features than Outlook tasks. Outlook lets you set a Start date, Priority, Completion Percentage number and more. Google Tasks have none of these. On the other hand, Google has a Task hierarchy. A task may be a subtask of another task. All these unique features of the individual systems are therefore technically impossible to synchronize. Here is a table that illustrates this point:

Feature\SystemGoogle TasksOutlookGogTasks
SubjectXXX
DetailsXXX*
State (done/not)XXX
Containing listXXX
Flat orderXXX
HierarchyX  
Due dateXXX
Start date X 
Priority X 
Reminder X 
Assigned to X 
Recurrence X** 

*) Only raw text. Not formatted text, bullet lists, images or attachments
**) Works as long as you never delete the task at Google, since Outlook creates a new task each time the recurrence triggers.

2: This may seem like obvious, but it's important to be aware of this to avoid losing tasks. After each synchronization, GogTasks remembers which tasks it synchronized. If you delete some of these from Outlook, GogTasks then interpret this as "Deleted from Google" rather than "Created in Outlook" - hence deleting the Outlook task. The history is also preserved after software upgrades.

Basically - if you're thinking "I'm going to delete all tasks at Google and to a clean re-sync": don't. This will result in you losing all Outlook tasks (given that this is not the first time ever you sync). If you do want to start over, there is a way though. Under advanced options you may click the Wipe history button to delete all synchronization history (not tasks), and with that start with clean sheets at the next synchronization.

3: GogTasks uses the system clock to determine where a task has last been changed. If your clock and Google's clock are minutes apart, you may experience synchronization going "the wrong way", leading to lost changes.

*) Text formatting will not be synchronized to Google because Google Tasks does not support things such as ordered list, bold text, attachments and images. The attachment and images will not be lost in Outlook though, even if you alter the task at Google and synchronize back. See this example.

**) The manual order of the tasks are actually kept in sync . If you remove all sort criterias in the Outlook task view, the tasks will appear in the same order at both Google Tasks and Outlook.