I see it often.

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Note added at 4 hrs (2010-10-09 23:34:23 GMT)
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It could also be a preface. See the following explanation:

A foreword is a (usually short) piece of writing often found at the beginning of a book or other piece of literature, before the introduction; this may or may not be written by the primary author of the work. A preface, by contrast, is written by the author of the book, although sometimes the two terms are used interchangeably. A preface generally covers the story of how the book came into being, or how the idea for the book was developed; this is often followed by thanks and acknowledgments to people who were helpful to the author during the time of writing. Often, a foreword will tell of some interaction between the writer of the foreword and the story or the writer of the story. A foreword to later editions of a work often explains in what respects that edition differs from previous ones.

If there is an author's preface as well, it follows the foreword. Unlike a preface, a foreword is always signed. Information essential to the main text is generally placed in a set of explanatory notes, or perhaps in an "Introduction" that may be paginated with Arabic numerals, rather than in the foreword. The word foreword was first used around the mid-19th century (originally used as a term in philology). It was possibly a translation of the Dutch "Voorwoord".
en.wikipedia.org/wiki/Foreword

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Note added at 4 hrs (2010-10-09 23:35:21 GMT)
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The reason I chose 'foreword' is that "prefacio" is preface.