In my view, there are two key metrics in social media that are needed to make something work. Influence and Engagement. Twitter needs people with large sphere’s of influence who have engaging content. That’s why when Oprah joined Twitter, their retention rates went up. She has a large following that finds her content (even in 140 characters) interesting and engaging. And while she still trails Ryan Seacrest and Ellen for followers (http://wefollow.com/), she has the influence and visibility to pull people in. So to increase the reach of Twitter, Twitter should run a recruitment campaign and then promote the engaging tweeters like Apple promotes apps to keep us engaged with our i-phone. Imagine the retention if Craig Venter, Jon Stewart, Tiger Woods, Salman Rushdie, Rick Steves, Eckhart Tolle, The Pope and Steve Jobs were tweeting regularly.