Crossbuilding on Debian for a derived distro

Toby Churchill Ltd is just one company basing their products on Debian and using cross-building to do it. The process has provided some challenges, including a transition from Familiar to Debian/Emdebian. I hope that others using the cross-tools and repository and build management tools would like to share experiences of how they build things, manage chroots and manage packages, to find out the better ways others are doing things, and what functionality really is missing. Managing cross-dependencies in a derived distribution set of build chroots is particularly difficult - discussion of how to fix this would be really useful.