I don't like waiting around for things to happen in the books I read. There has to be a hook, and then there has to be some event that catapults the main character(s) into the central conflict the story is built on. So that's why I sometimes skip blurbs altogether, if I like the reviews and the cover of a book.
They can take away the tension. If you ask me, a story should pull the reader in blurb or no, and hold them there on its own. But I've read several books whose back cover, inside flap, or summary (depending on the format) has told me all I need to know to guess at least some of the plot--and not only that, I have to sit around waiting for the main character(s) to catch on to what's happening, sometimes so slowly it's painful to watch them stumble about trying to get the hang of the situation.
Of course, it can go in the opposite direction, too. If there's just some dramatic, broad statement on the inside of the cover, that can deter me from reading the book if I think there's a chance it's going to follow an unoriginal plot, or there just simply isn't enough information about the characters and the rest of the story.
Have you ever skipped a blurb? How much do you think they help--or hinder? How much should a blurb give away about the plot and characters, before it says too much?
-----The Golden Eagle