The ability for members to add a topic to their Bookmark list when replying to a topic or when creating a new topic.
When creating a new topic, there should be a pre-selected checkbox next to the 'Submit' button. When they click Submit, the topic they created will automatically be added to their Bookmark list. They can opt out of this by uncheck the box before submitting.
This check box should also appear next to the 'Quick Reply' textarea (this is located at the bottom of each post, where users are able to quickly reply without having to to go to a separate page) and the 'Standard Reply Form' when they quote a person. When they click Submit, the topic they replied to will automatically be added to their Bookmark list. They can opt out of this by unchecking the box before submitting.
If the topic the user is replying to or quoting is already in their Bookmark List, then unchecking the box and submitting will remove the topic from their bookmark list.