I keep all customer info, as it comes in from CCBill and DHDMedia, in my own SQL table.

Then I write non-compilcated PHP scripts to create e-mail lists, or date history of new customers.

I also wrote, with professional help, a not-so-simple script that shows my customer addresses on a Google Map, complete with panoramic street view (the images photographed by the Google car).

Useful when selling tangible goods.