Most twitterers belong to other Social Networking platforms. A recent Forrester study showed that there was a fair amount of overlap between Facebook, LinkedIn and Twitter. No surprise there as I think many Twitterers would fall out as Creators or Critics on Forrester's Social Technographics ladder. Looking deeper into Facebook and LinkedIn, there are some interesting statistics. Facebook's Twitter fan page has over 7000 members with over 333 wall posts. There are 3118 people using the Twitter application, many of whom use the application to update their Facebook status directly from Twitter. There are another 30 applications that integrate some aspect of Facebook with Twitter.
On LinkedIn, over 500 people have included their Twitter username in their profile. Some like Dayna Marcum include it right in their own name. LinkedIn also has a robust group of Twitter members called Tweeple which has several thousand members. One of the most useful aspects of LinkedIn is LinkedIn Answers. Here members can ask questions that are answered by each other. There have been over 225 questions asked related to Twitter. A current question, about using Twitter for business, is below. Notice not everyone is drinking the Twitter Kool-aid as the first answer says it's useless! Of course, more experienced, useful answers have been provided to help the user.