I have only the vaguest idea what happens to my books after I've proofread the galleys. Here is an explanation of what my publisher's sales people do with them.
Interesting point--As a reader, I am not a fan of blurbs. As a general rule, I find that they have little or no relation to anything in the book, and they seem to me to just be an opportunity for the blurber to get some free marketing on the cover of the blurbee's book. However, this account makes it sound as if bookstore buyers may care about them.