WpRecipes.com - Daily recipes to cook with WordPress

Just paste the following code on your functions.php file:

add_shortcode( 'member', 'member_check_shortcode' );

function member_check_shortcode( $atts, $content = null ) {
	 if ( is_user_logged_in() && !is_null( $content ) && !is_feed() )
		return $content;
	return '';
}

Once done, you can add the following to your posts to create a portion or text (or any other content) that will be only displayed to registered users:

[member]
This text will be only displayed to registered users.
[/member]

That's all. Easy and useful!

Credits goes to Justin Tadlock for this awesome recipe!