I read a couple of NULL articles back-to-back today from SQLServerCentral. The first had to do wit the Four Rules of NULL and the second was NULL Versus NULL. Both were pretty good and picked up on how SQL Server uses and characterizes NULLs.
I can think of a handful or fifty times that the links to these articles would have been nice to have around to help explain why [FirstName] + NULL + [LastName] always came back as NULL. Of course, the enterprising developer would occasionally find the ANSI_NULLS setting as start asking questions about it. And as the author stated using SET ANSI_NULLS OFF is wrong... actually I think it's more like a sleight against God.