One thing I would like to see is the ability to assign people to more than one list simultaneously. I have 10 lists and want user X to be part of list 2,4,6...it is not possible to know this in one view.
The automation of ListMail is pretty standard, but the internal workings is what will make this product shine.
How about integration into BB or Cpanel?
I would like to see more custom areas set...like the ability to add birthdates. Via cron, a birthday reminder is sent to the people in our list.
The ability to send email from our computer 3rd party utility (Eudora, IE Express, etc.)