PowerDNS was the only DNS server at the time to use a relational database, and they supported several, including Oracle, which is what won me over. I embarked on an epic journey to make PowerDNS a first class citizen on Solaris 10. It took me five years, but boy did it pay off with massive dividends in stability and scalability!
PowerDNS isn't a perfect piece of software though: it has two major weaknesses, first that it is written in C++ as opposed to C and that made it a bitch to port to Solaris, and second that it depends on Boost, which is also a massive, bloated C++ monster which is a nightmare to get to build on any platform, let alone Solaris.
However, the software itself is a damn good DNS server, resistant to most attacks and constantly improving having had loving care from its user community, some which could be core PowerDNS developers in their own right. Finally it bears writing that the owners of PowerDNS are some of the kindest, sweetest guys one ever had the pleasure of working with, and they are open to considering suggestions and accepting contributions in patches and features. They were an absolute blast to work with over the years and could serve as poster children on how open source collaboration could work and make money off of at the same time.