Some businesses have intuitively latched onto the Twitter phenomenon for promotion and customer service; Twitter 101 is a new site aimed at helping everyone else get what the microblogging platform is all about.
Twitter 101 is written expressly for businesses. There are Twitter case studies from the likes of Pepsi, JetBlue, American Apparel, and Etsy. There's a section dedicated to Twitter best practices, and another that decodes Twitter jargon. Best of all, the whole thing is available in downloadable PDF slides for suits who prefer to print things out.
If you're looking for a guide that'll explain Twitter to you from a professional--not personal--standpoint, Twitter 101 is an excellent primer.