By default, the expression Yii::app()->user returns a CWebUser application component which represents the information that are closely related with the current user. Some information can be persistent throughout the current user session. For example, CWebUser already comes with a name property that stores the username of the current user.
Update: This wiki has been rewritten to be in line with Yii 1.1.14. Since many of the detailed complexities are now handled by Yii, the article focuses on how the crypt() built-in function works and why it's important to use it correctly.
I recently created a project called Yii-App on GitHub to kickstart my development of smaller Yii applications. The main goal of the project is to provide a ready-to-use application template that includes my bootstrap extension and many other useful extensions. After reading this article you will be able to use this project as a starting point for all of your Yii projects.