Let's say you're a mobile phone manufacturer, for example. Within Salesforce, you'll be able to search for any relevant "tweets" - for example, complaints about a broken phone - track any responses, and then use the company's Twitter account to respond yourself. Of course, you can already do all of those things within Twitter, but this makes the process more convenient, and, more importantly, allows you to capture that information and respond, all within a single application, one that lets you perform similar tasks on Facebook and elsewhere.