Django: "projects" vs "apps"
If so... in terms of Django's project.app namespace, my inclination is to usemyproduct.myproduct, but of course this isn't allowed  

There is nothing like not allowed. Its your project, no one is restricting you. It is advisable to keep a reasonable name.

I don't see any portion of my product being reusable in any context. Intuitively, I would call this one "application." Do I then do all my work in a single "app" folder?  

In a general django project there are many apps (contrib apps) which are used really in every project. 
Let us say that your project does only one task and has only a single app (I name it main as thethe project revolves around it and is hardly pluggable). This project too still uses some other apps generally.   
Now if you say that your project is using just the one app (INSTALLED_APPS='myproduct') so what is use of project defining the project as project.app, I think you should consider some points: 

There are many other things that the code other than the app in a project handles (base static files, base templates, settings....i.e. provides the base). 
In the general project.app approach django automatically defines sql schema from models. 
Your project would be much easier to be built with the conventional approach. 
You may define some different names for urls, views and other files as you wish, but I don't see the need. 
You might need to add some applications in future which would be real easy with the conventional django projects which otherwise it may become equally or more difficult and tedious to do.  

As far as most of the work being done in the app is concerned, I think that is the case with most of django projects.
I have a fairly complex "product" I'm getting ready to build using Django. I'm going to avoid using the terms "project" and "application" in this context, because I'm not clear on their specific meaning in Django.
Projects can have many apps. Apps can be shared among many projects. Fine.
I'm not reinventing the blog or forum - I don't see any portion of my product being reusable in any context. Intuitively, I would call this one "application." Do I then do all my work in a single "app" folder?
If so... in terms of Django's project.app namespace, my inclination is to use myproduct.myproduct, but of course this isn't allowed (but the application I'm building is my project, and my project is an application!). I'm therefore lead to believe that perhaps I'm supposed to approach Django by building one app per "significant" model, but I don't know where to draw the boundaries in my schema to separate it into apps - I have a lot of models with relatively complex relationships.
I'm hoping there's a common solution to this...