Dear Dr. pROfIt: Why Doesn’t Twitter Work?

Dear Dr. pROfIt: Like so many marketers, we're enthralled with social media. It just seems like we should be able to use this channel to encourage our customers to purchase from us. We started a Twitter feed 18 months ago — we announce discounts and promotions, link to articles that we write on our blog, etc. And for all of our efforts, we only have 374 followers. Sales from Twitter and our blog represent only 0.3 percent of our total annual sales. Are there folks out there who are successful using Twitter? If so, what best practices are they employing to increase return on investment?