In order to avoid bounce messages and unsolicited registrations, most webapps send automatic activation emails upon user registration, and the account remain inactive as long as it is not activated. Better yet, you can periodically purge your data by removing accounts that have not yet been activated.
Changing the way a CGridView is rendered from the configuration file, or through behaviors specified at the moment it is used, is handy to extend a CGridView without creating tons of different classes for it.
I am surprised that this is not in the default implementation, so I made my default CGridView implementation.
If you want to edit data directly in the gridview in a 'dropdownlist' style, then you could use the 'type' => 'select' option of TbEditableColumn (YiiBooster) or EditableColumn (x-editable for Yii). This wiki shows how to get data from the db for the 'dropdownlist', by converting AR model data into an array that is passed in json format.
This article shows a quick and easy way to implement flat user access control system. Flat means, that user access is controlled by level only, which is solution exactly opposite to complex RBAC access systems.