LinkedIn and twitter for business, facebook and soundcloud for social. Does soundcloud count a s asocial network?
Facebook, really. It works and it's popular. While it doesn't guarantee everything, it's a good start.
My favourite social network is Facebook because it is very easy to cummunicate with many people. It's very good for Seo. You can create a fan page and type many keywords for all pages.
I suppose it kind of counts but maybe not. LinkedIn has became really popular recently for business and many of the guru's have joined it and are available to connect with. It's fantastic!
using Facebook as my social network site. I prefer to use it in future. I connected lot of old friends through FB.
We use facebook since our site is a webshop which sell packaging machines and materials. We don't use twitter since there's really no point updating from time on what we are doing. but twitter can be pretty useful for a more "mainstream" businesses.
I use facebook for interacting with friends Linkedin for buisness and tumblr for Fun twitter for Politics