* The _validate hook and the _nodeapi('validate') hook of the node API (1) no longer take an 'error' parameter and (2) should no longer return an error array. To set an error, call form_set_error().
* The _form hook of the node module no longer takes a form hook and should not worry about displaying errors. Ditto for _nodeapi('form_post') and _nodeapi('form_pre').