I was browsing our twitter followers list earlier, and it struck me that a great deal of our followers are other authors, publishers and literary agents. We set up the feed to try and interact with potential readers of our book, but instead our twitter feed is full of literally thousands of other authors trying to push their own volumes.
Ideally twitter would allow an author to develop a fan base. It's all about building the relationships that make the reader feel emotionally involved. There's no point writing a story, no matter how clever, if the reader doesn't connect with it on some level.
Equally, if our twitter account is being used as a distribution platform as so many authors try to do, we never get those connections, and you therefore lose potential readers.
Twitter is about engaging, not broadcasting. Too many authors simply spam their twitter feeds with their Amazon/ nook/smashwords links to try and generate sales. For the most part this is counter-productive. No-one wants to feel like a product is being forced upon them, and followers who do feel like this can and do click the unfollow button with no regrets (or worse, report you as a spammer).
I am, of course, making sweeping generalisations - there are some fantastic authors out there that take time to chat with readers (and honestly, it doesn't matter what you chat about). If a reader feels valued not only will they buy your product, but their friends will too.
So don't just sell on twitter - listen too.