I'd like to see another drop down option in the Filter Rules to add an additional dedicated search area in addition to Subject, From, CC and To fields, a Delivered-To option.
The really nice thing about having a Delivered-To line in the header is that the address the message was sent to is always there even if the message was sent using BCC to remove the address from the To field, see the Gmail link below for an example.
This option would be a time saver over having to manually enter "Delivered-To:" ahead of each address you want to tag and is more accurate than just selecting "The entire header" and entering the target address.