In checking whether a form field contains an entry, it has been typical to do something like:
if (sizeof($form_state['values']['my_field'][LANGUAGE_NONE]) > 0)
because an empty field would still be an array, but an empty one. With entity reference fields, an empty field looks like:
$form_state values my_field und 0 target_id='' add_entityconnect_my_field_0_ = "New content" edit_entityconnect_my_field_0_ = "Edit content"
so that testing for the empty array fails. One could check to see if the target_id is empty, but I'm wondering if there's a way to test the form field for empty without needing to go down to that level.