The dependency based boot sequence uses the LSB fields in the header of each init.d script. This has removed several bugs in the former boot sequence, and now makes it easier to keep the sequence correct.
The advantage to using this method is that it allows a dependency resolver to maintain the actual order of the boot sequence instead of the package maintainers, eliminating conflicts due to statically defined sequence numbers on startup scripts.
In Debian releases prior to 6.0, a service could be added with update-rc.d:
update-rc.d mydaemon defaults