Is there also someone who made an import from vbulletin user notes to these user notes?
It was not that hard:
INSERT INTO xenforodb.xf_th_usernotes_usernote (user_note_id, message, post_date, last_edit_date, profile_user_id, user_id, username)
SELECT usernoteid, message, dateline, NULL, userid, posterid, username FROM vbulletindb.usernote;