80% of my clients run the same "master" version while 20% have minor customization's specific to their organization. I don't want to end up maintaining 20 diff

80% of my clients run the same "master" version while 20% have minor customization's specific to their organization. I don't want to end up maintaining 20 different applications, but being able to do minor modifications to the UI or data model on a per customer basis has been a nice selling point.