I was playing around with some of the smart mailboxes that I mentioned before, and I noticed a minor annoyance. Mail.app only has a global set of columns that are used for all messages list (excluding the Sent folders). So if you want to see the the recipient of the messages in the "Recently Sent" folder, the To column needs to be added to all folders.
Ideally, the list of columns would be a property of the message list itself. This will allow the "Recently Sent" folder to show the To column instead of From