I do have enough knowledge to weigh in on the & #39;twitter is useless for selling books& #39; thing but maybe I& #39;ll sit on it.
Ok I& #39;ll say something: the ones who say it& #39;s useless tend to be published by big five imprints and, importantly, they& #39;re YA writers. YA readers don& #39;t read small press or self-published titles and there& #39;s a correlation: this is to say, YA readers trend toward books that are--
--backed up by $$$ marketing, which includes but isn& #39;t limited to literally buying shelf space in B&N. For these writers, twitter isn& #39;t going to make enough difference. They& #39;re not after selling 10 or 50 copies; they & #39;need& #39; to sell 5000 or 10,000.
YA is also more dependent on libraries, especially school libraries. Again, it& #39;s a genre that doesn& #39;t really do well in any circumstance but & #39;backed by $$$$$$& #39; because that& #39;s the way YA readers pick books to read--via a lot of hype. And books backed by $$$$ need to sell a lot.
Small press and self-published writers, obviously, look at a very different scale and--save for larger small presses with enough $$$$$ for retail distribution--are not going to have titles in physical stores, and rarely in libraries.