Bind is the defacto DNS server out there, and the bind-dlz extensions enhances it even further by providing support for database backends. This simplifies the management of thousands of zones, and provides added redundancy (by way of database replication) and opens the doors for web frontends that ease this even more.
Bind DLZ on Rails is built based on our experience of managing thousands of DNS records through various (often crude) techniques, that included building zone files from databases via cron, and implementing PowerDNS for its database backends.
Nothing we tried seemed convincing, and we opted to go back to Bind using bind-dlz on a MySQL 5.0 backend. Using Rails 2 for a interface just makes sense because we can build a rich interface and an REST API in a single go.