Book Blurbs: Worth the trouble?

Every book has a back cover, which means something must be written on that back cover. What you'll usually find is a brief synopsis and some nice blurbs (unless you're Chuck Palahniuk, in which case, who needs a synopsis?), but how much do those blurbs mean? Should you take the time to write authors or reviewers you respect to ask them to blurb your book? (Or should you just ask anyone who'll say yes, and who cares who they are to you as long as someone else knows them?)

Stephen J. Dubner writes in his 2007 New York Times piece "How Much do Book Blurbs Matter?" that he used to give some credence to blurbs until, one day, he received a letter in the mail "along with the manuscript for a business book by two authors I don’t know. The letter was written by the book’s editor, another person I don’t know. Here’s the key paragraph:

If you find [redacted] and [redacted]’s ideas as compelling and inspiring as we do, a quote from you that we could print on the jacket would make a world of difference. I would be happy to help craft a quote if you prefer. My contact info is below."

Dubner writes, "I’ve come to believe [blurbs] really don’t matter at all, since most readers see blurbs as having about the same level of integrity as a used-car salesman’s personal promise that the car you’re about to buy is A-OK. But that might be an insult to used-car salesmen."