I was looking around the filter list when I noticed the action for "Remove extra Re: from subject' and decided to try it out. Wonderful. I configured it to work on incoming and outgoing messages, always and to let other filter continue to affect the message and then put it at the top of my filter list.
I do a lot of back-and-forth emails related to specific problem/solution/ project pairs and often the subjects are not carefully monitored in the dialog. It's wonderful to be able to automatically see them cleaned up. First Rate. It's like learning that your wife 'accidentally' made an extra bowl of creme caramel! Kename