Creating an options / settings page for plug ins

I’m working my way through the documentation on how to create an options page for a plugin, but there are huge gaps in my understanding (and perhaps in the documentation).

I understand that the whole register_settings thing is supposed to do most of the work for me, but despite hours on the codex and other sites, I still can’t get my options to save. They show up all right, but they don’t save when I update. What am I missing? There is no error message.

<?php

if ( is_admin() ){ // admin actions
	add_action( 'admin_menu', 'adminMenu' );
	add_action( 'admin_init', 'registerSettings' );
}

register_activation_hook(__FILE__,'registerSettings');
register_deactivation_hook( __FILE__, 'eraseSettngs' ); 

function adminMenu() {
add_options_page('Donut Settings', 'You have options', 'administrator', 'donut', 'donut_settings');
}

function registerSettings() {
  register_setting( 'donutOptions', 'optn1' );
  register_setting( 'donutOptions', 'optn2' );
}

function eraseSettings() {
  unregister_setting( 'donutOptions', 'optn1' );
  unregister_setting( 'donutOptions', 'optn2' );
}

function donut_settings() {
?>
<form method="post" action="options.php">
<?php settings_fields( 'donutOptions' ); ?>

Option 1
<input name="optn1" type="text" id="optn1ID"
value="<?php echo get_option('optn1'); ?>" />	

Option 2:
<input name="optn2" type="text" id="optn2ID"
value="<?php echo get_option('optn2'); ?>"  />
<input type="submit" value="<?php _e('Save Changes') ?>" />

</form>
<?php
}
?>