Project design / FS layout for large django projects
My current layout stems from me wanting to have a test-version of my sites.  This means having two projects for every site, since they need different configurations, and forces me to move all the applications out of the projects.
I've created two folders: $APP_ROOT/devel and $APP_ROOT/prod.  These contain all the apps.  Using source control (in my case git) I have the apps in devel at the HEAD revision, while the apps in prod are locked to the PROD tag.  The templates also have their own folder with the same layout as the apps.
Now I'm able to do all my development in the devel-apps folder and the matching template-folder.  When I have something I'm happy with, I tag that revision and update prod.
What is the best way to layout a large django project?  The tutorials provide simple instructions for setting up apps, models, and views, but there is less information about how apps and projects should be broken down, how much sharing is allowable/necessary between apps in a typical project (obviously that is largely dependent on the project) and how/where general templates should be kept.
Does anyone have examples, suggestions, and explanations as to why a certain project layout is better than another?  I am particularly interested in the incorporation of large numbers of unit tests (2-5x the size of the actual code base) and string externalization / templates.