Activity stream represent a user action within the site. A user can follow his/her own or friends activity within the site. Activity stream will be visible in each user profile. A user point system is calculated based on user activity. However with the new UserPoints system introduced, now user point and activity are no longer tied to each other. Each activity (new wall post, new blog entry, etc) can be assigned a point value through UserPoints API call. Please refer to UserPoints System for more details on how points can be given to user.