I was working on assignment which required me to access Tasks and show on customer portal. I written the apex code and fired SOQL, but to my surprise none of Tasks were fetched. I thought its a permission issue from profile or sharing access issue.
However at the end I found that there is a field on task object called IsVisibleInSelfService which derives the visibility of the tasks for customer portals. Even Apex code can’t find the task if this boolean field is not set to true.
Probably its trivial information but usefull when you are not aware of this 🙂