update_option DOES work for multisite

Just an FYI, you have this bit of code in your plugin:

// this is a hack because multisite doesn't recognize local options using either update_option or update_site_option...
if ( is_multisite() )
{
	global $wpdb;

	$multisite_prefix = ( is_multisite() ? $wpdb->prefix : '' );
	$q = $wpdb->prepare("
		INSERT INTO " . $multisite_prefix . "options
	        ( option_name, option_value )
	    VALUES ('hs_settings', %s)", serialize($opt));
	$wpdb->query($q);
}
else
	update_option('hs_settings', $opt);

This is completely unnecessary. update_option() works regardless of whether this it is a single site installation or a multisite installation.

update_option() = Option for individual site. Works on single site, or multisite. Only sets the option for the individual site within the network that it is called from.

update_site_option() = Option for entire network. Applies to all sites within the network it is called from. It’s just a wrapper for the newer update_network_option() function