How effectively social network marketing can replace display in stores and reviews in newspapers is an open question that won’t really be answered for a long time. The social networks are growing and there are already more possible outlets to work (Facebook, Twitter, Amazon, YouTube, Pinterest, GoodReads, and the comments section of every relevant blog are just the starting point) than most authors would have time to handle effectively (even assuming they have the skills and interest).Just because the author does a lot of marketing doesn't mean the publisher can't help - The Shatzkin Files
For any independent author, it's worth reading the whole discussion, and follow his links if you're really concerned with hearing all sides of the issue.
What we aim to do for marketing here at Thoth Books is to create one more social-network platform for our authors, in addition to the author's own postings in Facebook, Goodreads (which seems especially effective for authors) and other sites. Any book with the Thoth imprint will be displayed on our website and announced in this blog (with any links to the author's other works that he or she chooses). And we'll do what we can to get reviews. Will that make up for our absence from brick-and-mortar bookstores? Or will more of those stores begin to carry POD (publish-on-demand) books from small imprints? Even Mike Shatzkin doesn't know for sure. But all our efforts combined will certainly give the marketing a boost.