I dig the article Mike.  Way to explore an often-discussed topic more thoroughly than most of those discussions.

I guess it was pretty early on when I decided to embrace the NULL.  It's been easy enough to handle them in the application, and in a facade when I'm not responsible for the application. 

In one case, we got to the end of a project when a last minute requirement popped in requiring certain entities to own other entities.  We added a nullable FK to the entity being owned, referencing the owner.  Since the application was interacting with the database via SP's, we were able get the database ready in an hour or two.  That allowed us to spend the little time we had on the handful of minor changes to the application.

I suppose that anecdote may support the use of SP's more than that of NULL's, but I still dig NULL's