Great article on the Basics of iTVFs, Steve.
For those wondering about the performance of iTVFs that Steve mentioned, here's an article that discusses and demonstrates the performance advantage with code. It also provides an example of how to make a function that returns a scalar value using an iTVF.
How to Make Scalar UDFs Run Faster (SQL Spackle)
--Jeff Moden
Change is inevitable... Change for the better is not.