The civicrm_premiums_product table / object uses sort_position instead of weight. In order to implement the new Weight class methods - we need to modify the table schema and relevant code to use 'weight' like other "order-able" objects.
I've implemented CRM_Utils_Weight::addOrder for the selector - but it won't work properly until this change is made. Please test / verify the order changing behavior after completing the schema and code changes. (CRM/Contribute/Page/Premium.php line 185+).
The URL for this selector is http://.../civicrm/admin/contribute?reset=1&action=update&id=$pageID&subPage=Premium