I use Facebook, Twitter, and Linkein - because of the way it allows business owners to setup a business page, interact with your friends and fans, and their ads are way cheaper than Google Adwords.
I really enjoy seeing my fan page likes increase every day. Also, reviewing the info of the people who like my page gives me great underground research.
This also increases my potential client base. Of, course you need to be posting at least twice a day to reach your connections.