If you're with a publisher, I agree with those who have already posted. However, if you're self-publishing your book and you are looking for a blurb from another self-published author, I think it's easier to get a blurb. They may not be famous, but maybe they have a decent fan following. I wouldn't recommend this with huge authors in the self-publishing world like Konrath or Hocking because it's the same kind of thing--unless you know them personally, it's something you don't really do. So maybe you don't even care about my advice to get a "less famous" author's blurb, but here it is anyway. . .
I did this with my self-published novella with another author who had a similar book in a similar genre. She's not huge, but she has about 500 blog followers, and her books have been pretty well received. I just sent her a very polite e-mail asking if she could offer a blurb that I could use on my cover or in my description. I told her why I felt our books were similar and why readers of her books might enjoy mine. I pasted the book description, linked to a few spots around the web (the first chapter on my blog, the trailer, the Amazon listing, etc.), and told her if she was too busy or uninterested, I totally understood. Fortunately, she was interested, so I gifted her the book and about a month later she sent me something to use. I have no idea if it's had an effect on sales, but I'm still glad I did it.
So, hopefully that helps even if it wasn't exactly what you were looking for.