I did some things on Twitter and Yammer (inside my company), but to be honest it does not work for me. Best social networking tool for is and will be LinkedIn. It is professional and adds value with its features. For instance asking questions or start discussion inside groups. I truly like that and it works for me. Yammer account is gone and twitter to (at least I am trying to).
I will try some other time to get rid of it. I know it is an hype this kind of social networking, but not for me. I stick with LinkedIn and Facebook to stay in touch with my Canadian, English, US friends and family.