I needed a tool that was super simple to transfer email from a non-cpanel server to a new WHM-based VPS. Ended up coding one and launched http://transfermyemail.ca - have had a few server companies jump on board because they needed migration tools too! Was it worth it from a development time point of view? Not yet...maybe next year :)

When you're picking up your kid from school and you bump into a client... "Hey, I know you're not working but have a quick question for you."