In addition to the standardized opt-in preference of What types of email would you like to receive from us has anyone implemented How often would you like to receive emails from us: Monthly, Weekly, BiWeekly as a secondary opt-in preference?
If so, how in a nutshell do you manage this rotation of preferences without duplicating or dropping people from the list? Do you assign someone an attribute of "Monthly",etc then just suppress them out each time?
Has anyone found this system ultimately useful or more trouble than it's worth? Does it make a difference to people opting in?