gistfile1.php

/**
 * In the config
 */
return [
	'components' => [
		'urlManager' => [
			'rules' => [
				//....
				//let's assume 'view' is not eligible for a username :)
				'member/<username:\w+>' => 'member/view',
				//....
			]
		]
	]
];

/**
 * In the controller
 */
class MemberController extends \CController {
	public function actionView($username){
		$user = User::model()->find([
			'condition' => 'username = :username',
			'params' => [
				':username' => $username
			]
		]);
		if ($user === NULL){
			throw new CHttpException(404);
		}
		$this->render('view', [
			'user' => $user
		]);
	}
}