I can tell quite a bit about it without reading the blurb. To me, the blurb is a spoiler too often. I will know whether the book is horror, science fiction, fantasy, thriller, etc. just from the cover, where it is shelved, etc. There are often reviews at the front of the book that don't give away the story, so I'll look at those. I'm not picky about the genre as long as it is an engaging, well-written story, so if I can see enough to tell that it is probably a good book, I don't really care to know exactly what it is about when I start reading. I'd rather learn that along the way. While I am reading it. I hate blurbs
I'm uncomfortable without a blurb. They're like grabbing onto a pair of familiar love-handles. The badly-written and poorly-thought-out blurbs that tell you at least half of the story make me want to strangle whoever wrote it though.
I usually only read the very start of the blurb, the bit that says things like "in 17th century Britain, a girl of nobility, Harriet..." then I will shelf it because it's not my cup of tea. If I feel like I am interested in the character and their life I won't read the end of the blurb because as Steerpike said, it reveals too much. Even though I have plenty of favourite writers, I am a fan of browsing all sections and genres (except fantasy). I would rather have a few books stacked up in my 'To Read' pile of unknown authors than tried and tested writers.
if the blurb and cover do not entice me when just picking randomly through books, rather than looking for something specific, then i dont buy it! So I read the blurb because it can make or break whether I buy it/read it!
I especially hate when the blurb does not match up with what the story is like, as I feel I was misold the book - hence my (and my husbands) deep hatred for Scarlett Thomas' 'The End of Mr Why' - the blurb made it sound good but the story was nothing like it and was the worst book I have ever read.
Then you would hate the blurb for The Harvard Lampoon's Bored of the Rings. It's a steamy scene between Frodo and a female elf, and the scene appears nowhere in the book. Of course, that too is a joke in one of the funniest parodies ever penned. Or rather, in a hilarious spoof. Okay, okay, a mildly amusing cheap ripoff...
The blurb is what makes me want to read the book. I go into bookshops and pick random books off the shelves and read the back. If I like the sound of it, I'll buy it. Also, with any book I read, I have to read the back or I'll feel like I haven't read the whole book. I read every bit of info in a book - even the copyright info! lol