It is difficult to perform user dependent theming through a general configuration in 'main.php'.
This article proposes a method to do so through a Factory that dynamically generates classes to allow delayed resolution of actual user values.
This means that you can refer to values that are stored in the database through the CActiveRecord before Yii is actually loaded.
The values will be fetched from the database when actually used for the first time, which is after Yii is loaded.
Actually, you can use pretty much any method that relies on Yii with this method.
You would find having such a need in most Yii Projects. Your database needs a specific format to store date fields, while you may want to display it in different formats to the users on forms and other views.
Authentication and Authorization is a good tutorial. Among other topics, it describes basic aspects of Yii's RBAC implementation. But however hard I read the tutorial, I couldn't understand how exactly the hierarchy works. I found how to define authorization hierarchy, how business rules are evaluated, how to configure authManager, but almost nothing about how I should build my hierarchy, in what sequence its nodes are checked, when the checking process stops and what would be the checking result.