wp-add_filter-example.php

gistfile1.php

/**
 * Test lowercase 
 */
function tolower_filter($text) {	
	return strtolower($text);
}
add_filter('the_content', 'tolower_filter'); 

/**
 * Test more
 */
function thirtyten_excerpt_more($more){
    return '&nbsp;… <a href="'. get_permalink() . '">' . __('finish reading '.get_the_title() .'', 'twentyten') . '</a>';
}

remove_filter( 'excerpt_more', 'twentyten_excerpt_more' );
add_filter ('excerpt_more', 'thirtyten_excerpt_more' );

@see http://aaron.jorb.in/blog/2010/04/introducing-thirty-ten/