I've been reading back posts at Shrinking Violet Promotions. I've gone through this past May's (the blog has only been around since February), where I found a two-part interview with Brent Hartinger. The whole point of this particular blog is to encourage writers who are not born performers/promoters, but as one of those, I have to say I found the Hartinger interview a bit of a downer.
In Part One of the interview, pay attention to Hartinger's responses to Question 6, "Is there a window of opportunity for book promotion? A length of time after which one’s efforts make little difference?" and Question 11, "How much impact do you think an author's efforts can actually have on sales?"
Sadly, I think he's probably right on the money with everything he has to say. That doesn't make me enjoy hearing it, though.