Leaving LHR for IAD early this year, I asked the UA check in agent if she could put priority tags on my and my partner's bags. She replied that they don't use them on international flights, and they don't have any effect. This coming from someone who staffs the Business counters. Idiots! In any case tags wouldn't have helped as I was stuck in the "pit of hell" for a good few hours before I even saw my bags again.