Quotes from respected critics, I like. Quotes from respected critics on the quality of the translation, I really like.
Quotes from other authors: HOLY SMOKE are these annoying. I don't care if you're friends with a famous writer; that tells me nothing. If a cover only has those blurbs I'm actually disinclined to pick it up.
Be especially wary of any book bearing a quote from Gary Shteyngart, one-man blurb factory. Some authors like A.J. Jacobs have even been coming clean about their prolific and unwaveringly positive blurbs lately.