we've discovered that by quick jumping to a specific task it brings up a detail sheet for that task that has a UI button for adding a note linked to that task (ie as opposed to the parent entity it itself is linked to)
strangley there doesn't seem to be any other method of doing this - ie adding notes via a list view of tasks for instance (there doesn't seem to be anyway to navigate to the task detail sheet either from any of the task list views, you have to use the quick jump feature)
adding notes to specific tasks seems to be something that people here would want to do frequently :)