Link to a Planet Virt Tools which is a collection of bloggers talking about Linux Virtualisation.
To go along with that is an amazing collection of Debian Build Tools, which includes things like debootstrap, qemubuilder, debian-installer, virt-inst, debootstick, Kameleon and a bunch of others.
Buiding Debian Images talks about various ways of building debian based images. The slide show mentions bootstarp-vz as the way many providers build their images.