Perhaps that's being a bit harsh.
The point is, forewords should put a high-gloss shine on the concept and execution of the book. Foreword authors should meet a few basic goals:
- Promote yourself. Readers should understand right away that you what you're talking about. If you've published in the field or won awards for pertinent work you've done, say so. Don't be modest.
- Say great things about the book's author. If you know the author, or at least one of them, say so. Give some insight into why you respect the author and trust him (or, you know, her) to create the best book possible on the subject.
- Say great things about the book. This is where you need to actually have a copy of either final manuscript or page proofs. Page proofs are printed or PDF documents that show exactly what the final product will look like, including images, page numbers, and so forth. Take a close look, overlook any typos, and try to paint for the reader a portrait of all the great content they'll find in the book.
- Finish with a prediction of success. Surely potential buyers who purchase the book and study it will learn in a new way, succeed beyond expectations, win the envy of their peers, and save the entire planet from almost certain destruction. Or something like that.