http://who.godaddy.com/whois.aspx?domain=diigo.com&prog_id=GoDaddy does not match
http://who.godaddy.com/whois.aspx?domain=diigo.net&prog_id=GoDaddy
BUT, the diigo.com was last updated on the 25th that matches up with the hijacking - seems to me just up date your dns records.
