I've been hearing a lot of discussion lately about the value of a book review (and by extension, book blogs). Are they actually helpful, and do they really sell books? Word of mouth has always been a powerful promotional tool, but if Joe Schmoe decides he knows which books are awesome and which fail on pretty much every level, and shares his opinion with the world, is that actually any more effective than if he just made a personal recommendation to a few friends?
Obviously I think book reviews can be useful, or I wouldn't be here. I do think, though, your mileage can vary by the kind of review.
I'll admit to being picky about what kinds of reviews I read. I have very little interest in the reviews of my local newspapers, since they vastly prefer literary fiction and seem to write the reviews to appeal only to the most pretentious snobs (or, I suppose, to the type of reader who wishes they read more intellectual fare). They also all kind of end up sounding the same. Newspapers are at a disadvantage, in a way, because they're limited to how much space they can take up in their review, so they're often written to be very short and never actually give enough information to snag my interest as a reader.
Similarly, I tend to skip over the reviews that basically consist of the plot summary from the back of the book. No thanks, I can dig up that much info on amazon if I want.
In my never humble opinion, book blogs have an edge when it comes to review territory, for a number of reasons. We're free to choose what types of books we want to review, and we're not limited by space. We're not paid for the reviews we write, so you know you're getting our honest opinion, whether that includes ranting or fangirly squeeing. Best of all, though, and what really makes the value for book blogs and their reviews, is you guys. Reviews on blogs are the opening to a full readerly discussion, not a statement of "I know all and therefore my opinion is what you need to know." It's the community that gives these critters validity, knowing you're getting the thought-out opinion of not just one person, but every one of you guys who pops by and has a thought on the subject.
Booya.
Obviously I think book reviews can be useful, or I wouldn't be here. I do think, though, your mileage can vary by the kind of review.
I'll admit to being picky about what kinds of reviews I read. I have very little interest in the reviews of my local newspapers, since they vastly prefer literary fiction and seem to write the reviews to appeal only to the most pretentious snobs (or, I suppose, to the type of reader who wishes they read more intellectual fare). They also all kind of end up sounding the same. Newspapers are at a disadvantage, in a way, because they're limited to how much space they can take up in their review, so they're often written to be very short and never actually give enough information to snag my interest as a reader.
Similarly, I tend to skip over the reviews that basically consist of the plot summary from the back of the book. No thanks, I can dig up that much info on amazon if I want.
In my never humble opinion, book blogs have an edge when it comes to review territory, for a number of reasons. We're free to choose what types of books we want to review, and we're not limited by space. We're not paid for the reviews we write, so you know you're getting our honest opinion, whether that includes ranting or fangirly squeeing. Best of all, though, and what really makes the value for book blogs and their reviews, is you guys. Reviews on blogs are the opening to a full readerly discussion, not a statement of "I know all and therefore my opinion is what you need to know." It's the community that gives these critters validity, knowing you're getting the thought-out opinion of not just one person, but every one of you guys who pops by and has a thought on the subject.
Booya.

Comments
You touched on all the aspects that give us bloggers an edge over the professionals: unlimited space, freedom to review whatever we want, having no ulterior motive to bias our reviews, and the community aspect. I think the best book-bloggers post frequently (I'm trying to do better at that) and try to read widely.
On the other hand sometimes I'll notice that ALL the reviews from a reviewer are positive. Then I just don't believe them anymore. Especially if they rave about a book I read and I didn't like it.. then it sort of gets filed under my "crazy review" folder. There are certain blogs I feel like the only reason people read the blog is for the free books, not for the reviews. Oh well. Then there are people who's tastes are so different - they gave something an A and I read it and think "C", but they still count in the "buzz" for a book - if enough people are saying things, I want to try the book.
I do think individual book blogs are "legitimate", whatever that means. I review books, myself, on my own LJ. Granted, some reviewers are much more well-read than others, have a better handle on the genre/s they read and review, and have a good balance between the plot, the structure, the characters and the overall "mood". I find THIS blog does that wonderfully. Even if I find I'm not interested in the book when I finally get to it in the bookstore, still, it helps with a possible reading list.
Maybe I'll start doing what y'all do: post the short impressions, then have the longer review behind the cut. I tend to rattle on at length.
(Now, as for how valid the reviews are, it depends. There´s a lot of people who´re just going with the flow an bashing books because all the cool kids are doing it. Same with positive reviews.)
If I've already bought a book because it caught my eye etc., then I avoid reviews because I've already decided to read it; but I can't count the number of books I've read that I never would have read if it weren't for other people's reviews, especially on LJ, Blogspot (Blogger) and Goodreads.
I love this chance of sharing that the internet gives us, and taking book reviews out of the monopolising and snobby hands of "professional" literary reviewers and, yeah, giving the power to the people ha ha that the internet has given us. I find fellow readers' reviews better than the "professional" ones, where the reviewers are often preoccupied with asserting their literary laurels and showing off with clever allegories and fancy literary elusions...
Oh I do get carried away don't I? ;)
I fail to see how that is different from reading a review on your blog, reflecting that our tastes seem to converge on x, y, and z books I've read that you reviewed, so, hey--maybe this is a book that I'd enjoy too. The only difference is that I've never met you in real life, and you're not recommending books specifically to *me.* But, hey. I've got a friend who I've never met in real life, but we've been IMing for about 12 years now, and over the years we've discovered that, except for a certain number of classics and the fact that I'm addicted to romance novels but he isn't, we have very nearly identical lists of titles on our shelves. Well, and of course, there's my collection of cookbooks. Poor boy couldn't find his way around a kitchen with a map, and I like WWI-era cookbooks and really odd ones--my favorite is a bread book from the Tassajara Zen monastery in California. Zen plus the art of baking bread is a bit of a mind-twist.
I'm also glad that I'm not the only one who tends to skip long reviews or at least just skim them to get the best and worst points.
"Are they actually helpful, and do they really sell books?"
Is there any research about if offline reviews actually sell books? Is there any research about if offline reviews are helpful? I tend to be skeptical of any unexamined assumptions. Offline reviews might be the venue that people are *used to* but that's not the same thing.
I guess it all comes down to what do you value. If the only thing you (general you, of course) is money, then you probably can't see much point in any hobby.
"We're free to choose what types of books we want to review, and we're not limited by space. We're not paid for the reviews we write,"
I agree with these points and also with the discussion. I'd like to also add another benefit that bloggers usually have. Usually, a reader can quite easily see what other books the blogger has reviewed and her/his opinions about them. Also, often bloggers provide further information about their reading tastes such as favorite authors, books, and genres. I even mention that I favor characters, atmosphere, and the setting over plot. If you don't know an offline reviewer's tastes beforehand, there's no way to get that info.