If you often use functions such as update_option, update_post_meta (or any meta-function for that matter) it might be useful to know that the value you pass can be mixed.
The value is serialized before it is saved, which in short means that it is converted to a string.
$arr = array("mixed array", "of" => "different values"); add_post_meta(1, "serialize_test", $arr, true); $meta = get_post_meta(1, "serialize_test", true); echo "<pre>"; print_r($arr); echo "\n"; print_r($meta); echo "</pre>";
Array (  => mixed array [of] => different values ) Array (  => mixed array [of] => different values )
So it is very useful to know this, and even more useful to know that sometimes even the WordPress Codex can be wrong!