You should know by now that, with me, nothing is black and white. So, here’s my answer.
Occasionally, there is some redundancy when you have the same certain people in more than one of your networks, but that is more the exception than the rule – not to mention that those folks are usually die-hard online networkers, and they tend to really ‘get’ what you are doing with your broadcasts. And, if they’re following you in all of those places, they really like you and will just be happy to hear from you.
So, on this question, I lean heavily towards the ‘you need to belong to many social networking sites’ side. Simply because there are a gazillion people online and they choose to belong to different social networks because each network presents a specific personality, attitude and interaction capability – oh, and that’s where their friends play. As a result, when you decide to belong to a variety of networks, you are reaching a more diverse audience. You are reaching the Twitter people, the Facebook people, the LinkedIn people, the Tagged people, the Squidoo people, the de.licio.us people – and you are reaching them where they are.
To participate on multiple networks is to build, activate and inspire multiple audiences and to foster a bevy of solid relationships. My raison d’etre exactly.