I've always wondered why self-published authors don't do more online advertising like this. I think the quick answer is that they don't even know where to start. This overview is a nice overview of some of the basics, and even taught me a few things. For example, I didn't know that anyone could purchase a review from Kirkus.
Just as agencies have emerged to help businesses with social media marketing, I wonder if we'll start to see the emergence of marketing agencies specifically geared toward online promotion for self-published authors. (via)