After the books on dragons, D&D monsters, wizards and faeries, Wizards of the Coast/Mirrorstone apparently saw that vampires were hot due to Twilight (which is name-checked on the back cover and with an explicit reference to Forks at the end of the book) and thought that D&D vampires were ripe for a Practical Guides book.
Unfortunately, the vampires of the Dungeons & Dragons world have been a mess since they first debuted in the 1970s, and they're likely not what tweens interested in vampires now because of Twilight, the Vampire Diaries and Monster High are looking for.
First off, and most obviously, it's a world that has wizards and magic in it, and no modern technology. This is addressed in both the art -- which is the usual mix of work for previous D&D books and new work commissioned just for this one -- and explicit mentions of magic items and wizardry. I've never been a pre-teen girl, but my gut says this isn't what they're expecting if they go looking for a parent-approved book that lets them touch on some of the concepts raised by the Twilight books and movies.
Second, D&D vampires don't actually drink blood as a general rule. (They can, but it's more of a flavor choice by the Dungeon Master.) They "drain energy," mechanically making their opponents weaker mid-fight. While this is possibly useful in a D&D game (I think it's an antiquated approach that should have been ditched years ago in favor of more thematic attacks, like those of Ravenloft's Nosferatu vampires), it doesn't line up at all with the classical vampires that non-D&D readers will be expecting. To Lisa Trutkoff Trumbauer's credit, she keeps references to energy drain to a bare minimum in the latter half of the book, but they're still there, and will likely baffle most casual readers.
All of that said, for someone like me, who's collecting these as introductory works to get his young kids into the D&D game in a few years, this is a pretty good book, although lags far behind the dragons, wizards, faeries and monster books. (I haven't read the dragon magic or dragon riding books so far.) It looks like Mirrorstone may have discontinued this series, which is a shame, because I'd love to see giants get this same treatment (they're a group of monsters that have been strangely under-examined by D&D historically), along with dungeons as a milieu.
(I also wouldn't mind an index, either in the book or online, that identifies where the magic items and other monsters referenced came from originally. As with the Practical Guide to Faeries, a fair number of them are new to me, and I suspect came from either later third edition D&D books or fourth edition ones, and I'd love to check them out.)
If you know what you're getting -- and what you're not -- with this book, this is a worthwhile purchase, but I'd put it quite a bit behind the Practical Guide to Dragons, Practical Guide to Wizardry and Practical Guide to Faeries, and a little behind thje Practical Guide to Monsters.