I'll go first, although I have huge doubts about my own entry:
A perfect blurb inspires you to buy the book, but *not* through deception.* It gives you the essence or the spirit of the story, without telling you the story itself. And by essence, by spirit, I mean it gets across the ideas or the feelings that inspired the author in the first place: the bits that make it special.
*Deception may lead to you throwing said novel at delicate wall.