The jacket blurb's a weird tradition, when you think about it. For me, it's kind of become like a word said in such repetition that all meaning and intent get lost, rendering said word--or the act of blurbing--some weird, standalone thing. Blurbs are ostensibly there to recommend the book for you, to describe it for you in a far-flung fashion that doesn't quite describe anything, in case the paragraph-or-more description on the back of the book hasn't sufficiently ensorcelled you. And I think these blurbs actually do work. Most of us need nudges, I think, confirmation that our choices will be the correct ones. More often than you'd think, I've had customers ask me to look up a certain book on Amazon and recite the customer reviews for it.
But here's the secret of blurbs: more often than not, they're written by the author's buddies, or former teachers. If you're feeling idle one day, pick up your favorite book of literary fiction and do a contrast and compare between the acknowledgements and the blurbs. Feel free to go so far as to circle the similarities.
The above documentary, which speaks clearly while having its tongue in its cheek, exposes one of the most prodigious blurbers, Gary Shteyngart, author of everyone's favorite, Super Sad True Love Story. I noticed the prominence of Mr. Shteyngart a while back, and this collection of his blurbs along with the documentary wonderfully confirmed my suspicions.