first, let me thank Anders again for his work on debian-build-cloud(ex-ec2debian-build-ami), that gave us the momentum which is essential
to get started.
One almost tautological advantage of using Debian-Installer is that the
resulting system will be the same as any other Debian system installed
following the instructions on the Debian website.
One of the largest difference is that Debian-Installer is booted as an
operating system, and debian-build-cloud is executed as a program from a
running system. In the case of preparing cloud images, the impact of this
difference is reduced. On the Amazon cloud for instance, I prepared machine
images of the Debian installer. When booted and provided a preseed file, they
install a Debian system on a target volume. What blocks me from producing a
usable image is that Debian-Installer does not seem to support making
partition-less systems (and maybe it is not even a problem if it is possible to
boot partitionned volumes on the Amazon cloud). Once this is solved, I think
that we should seriously consider using Debian-Installer.