Customization
A custom system allows me to make changes, adding or removing as I need to. I like trying new things as additions to my systems. Papers, cards, pens. Early last year I even tried a system based around an iPad.
System Failure
When I have job changes, or major life changes I find that my systems fail. My solution is to stick to The Middle Way Method, and create a new productivity tool. I can usually create a new tool in a weekend.
Creating your own productivity system will help you to be successful with your efforts to be more productive. When your efforts get hung up you can give yourself a fresh start.