What Does it Mean to be Reformed?

In an effort to understand how churches in the same denomination (PCA) can be so different, I picked up this book. It's a collection of essays covering the 3 major strands of the American reformed church: Princeton, Dutch, and Southern Presbyterian. Each background has an introductory essay and 2 or 3 essays on crucial men in that strand and their theology.

To boil down my notes on the book to the length of a typical blogpost, I'll say that the book does a great job explaining the distinctions of the 3 backgrounds in view, but at the end I'm left with the feeling that there's a large group of people that call themselves reformed that wouldn't identify with any of the three groups. It seems there should have been some discussion over the large number of reformed Baptists, or used-to-be-Baptist reformed folks. These are the kind of folks that we most often meet in the PCA and undoubtedly have added to the uniqueness of American reformed theology and practice.