Do you have a blog or website where you share your experience of hosting your DNS using PowerDNS? I made some efforts but was not able to get it to work properly.
Post on relevant forums, SEO efforts and provide good quality service. It is always more beneficial to keep the customer than going out and look for new customers.
Hosting providers do use the word 'unlimited' a lot since they usually assume that normal users will not have the need to consume a certain amount of data. As long as your service is running smoothly, you should not worry too much about it.