Also, you can submit entire arrays with forms, and PHP will interpret it.
IE:
<input type="text" name="var[0]" value="data">
<input type="text" name="var[1]" value="data2">
will be treated like the following upon submission:
$var = array("data", "data2");
I've even used it for two dimensional arrays, and associative arrays (name="var[subvar][0]").
This can come in handy.