That is the question a lot of self published authors, including myself, are asking. We know the gold rush is over and now it is harder than ever to move our books. Dave Zeltserman has a few thoughts here in a piece well worth reading.
One thing really jumped out at me since I do so many reviews. He writes:
"Online book reviews: Web reviews seldom sell more than a couple of books--print or ebook the same."
While I don't think it is the responsibility of a reviewer to sell books (or stop somebody from buying a book either) it is rather depressing to have what amounts to be so little impact.